CHAPTER VI.. Ancient Glaciers in the Eastern Hemisphere.

ANCIENT GLACIERS IN THE EASTERN HEMISPHERE.

About two million square miles of northern Europe were covered with perennial ice during the Glacial period. From the scratches upon the rocks, and from the direction in which material has been transported, it is evident that the main centre of radiation is to be found in the mountains of Scandinavia, and that the glaciers still existing in Norway are the lineal descendants of those of the great Ice age.

So shallow are the Baltic Sea and the German Ocean, that their basins were easily filled with ice, upon which Scandinavian boulders could be transported westward to the east shore of England, southward into the plains of Germany, and eastward far out upon the steppes of Russia. The islands north of Scotland bear marks also of an ice-movement from the direction of Norway. If Scotland itself was not overrun with Scandinavian glaciers, the reason was that it had ice enough of its own, and from its highlands set up a counter-movement, which successfully resisted the invasion from the Scandinavian Peninsula. But, elsewhere in Europe, Scandinavian ice moved freely outward to the extent of its capacity. Then, as now also, the Alps furnished centres for ice-movement, but the glaciers were limited to the upper portions of the valleys of the Rhône, the Rhine, and the Danube upon the west and north, and to a still smaller area upon the southern side.

MAP showing

GLACIATED AREAS

in North America and Europe.]

Central and Southern Europe.

The main centres of ice-movement in the Alps during the Glacial period are the same as those which furnish the lingering glaciers of the present time. From the water-shed between the Rhine, the Rhône, and the Aar, glaciers of immense size descended all the valleys now occupied by those streams. The valley of the Rhône between the Bernese and the Pennine Alps was filled with a glacier of immense depth, which was maintained by fresh supplies from tributaries upon either side as far down as Martigny. Glacial markings at the head of the Rhône Valley are found upon the Schneestock, at an elevation above the sea of about 11,500 feet (3,550 metres), or about 1,500 feet above the present surface of the Rhône Glacier. At Fiesch, about twenty miles below, where tributaries from the Bernese Oberland snow-fields were received, the thickness of the glacier was upwards of 5,000 feet (1,680 metres). Near Martigny, about fifty miles farther down the valley, where the glacier was abruptly deflected to the north, the depth of the ice was still upwards of 1,600 metres. From Martigny northward the thickness of the ice decreased rapidly for a few miles, where, at the enlargement of the valley above the head of Lake Geneva, it was less than 1,200 metres in thickness, and spread out over the intervening plain as far as Chasseron, with a nearly level surface, transporting, as we have before said, Alpine boulders to the flanks of the Juras, and landing them about 3,000 feet (1,275 metres) above the level of Lake Geneva. The width of the main valley is here about fifty miles, making the slope of the surface of the ice about twenty feet to the mile.

From its "vomitory," at the head of Lake Geneva, the ice of the ancient Rhône Glacier spread to the right and to the left, while its northern boundary was abruptly terminated by the line of the Jura Mountains. The law of glacial motion was, however, admirably illustrated in the height to which the ice rose upon the flanks of the Jura. At Chasseron, in the direct line of its onward motion, it rose to its highest point, while both to the southwest and to the northeast, along the line of the Juras, the ice-action was limited to constantly decreasing levels.

Down the valley of the Rhône the direction of motion was determined by the depression of Lake Geneva, at the lower end of which it received its main tributary from Mont Blanc, which had come down from Chamouni through the valley of the river Arve. From this point it was deflected by a spur of the Jura Mountains more and more southward to the vicinity of Culoz, near the mouth of Lake Bourget. Here the glacier coming down from the western flanks of the Alps, through the upper valley of the Isère, past Chambéry, became predominant, and deflected the motion to the west and north, whither the ice extended to a line passing through Bourg, Lyons, and Vienne, leaving upon one of the eminences on which Lyons is built a boulder several feet in diameter, which is duly preserved and labelled in the public park in that portion of the city. Farther south, glaciers of less extent marked the Alps most of the way to the Mediterranean, but they were not at all comparable in size to those from the central region.

To the right of Lake Geneva the movement started by the Rhône Glacier spread eastward, being joined in the vicinity of Berne by the confluent ice-stream which descended from the north flank of the Bernese Oberland, through the valley of the Aar. These united streams filled the whole valley with ice as far down as Soleure.

GLACIAL MOVEMENTS

IN FRANCE AND

SWITZERLAND.]

Farther eastward, other ice-streams from the Alps became predominant, one of which, moving down the Reuss, deployed out upon the country lying north of Lucerne and Zug. Still farther down, the ancient glacier which descended the Limmatt spread itself out over the hills and lowlands about Zürich, one of its moraines of retrocession nearly dividing the lake into two portions.

Guyot and others have shown that the superficial deposits of this portion of Switzerland are just such as would be distributed by glaciers coming down from the above-mentioned Alpine valleys. Uniting together north of Zürich, these glaciers pushed onward as far as the Rhine below Schaffhausen. In Frickthal the glacial ice was still 1,200 feet thick, and at Kaisterberg between 400 and 500 feet.

At Lucerne there is a remarkable exposure of pot-holes, and a glaciated surface such as could be produced only by the combined action of moving ice and running water; thus furnishing to tourists an instructive object-lesson. Among the remarkable instances of boulders transported a long distance in Switzerland, is that of a block of granite carried from the Valais to the vicinity of Soleure, a distance of one hundred and fifteen miles, which weighs about 4,100 tons. "The celebrated Pierre-à-Bot, above Neufchâtel, measures 50' × 20' × 40', and contains about 40,000 cubic feet of stone; while the Pierre-des-Marmettes, near Monthey, contains no less than 60,840 cubic feet."

The ancient glacier of the Rhine, receiving its initial impulse in the same centre as that of the Rhône, fully equalled it in all its dimensions. Descending eastward from its source near the Schneestock to Chur, a distance of fifty miles, it turned northward and continued forty-five miles farther to the head of Lake Constance, where it spread out in fan-shape, extending northwest to Thiengen, below Schaffhausen, and covering a considerable area north and northeastward of the lake, reaching in the latter direction Ulm, upon the Danube--the whole distance of the movement being more than one hundred and fifty miles. Through other valleys tributary to the Danube, glaciers descended upon the upper plains of Bavaria, from the Tyrolese Alps to the vicinity of Munich. From Gross Glockner as a centre in the Noric Alps, vast rivers of ice, of which the Pasterzen Glacier is the remnant, poured far down into the valleys of the Inn and the Enns on the north and into that of the Drave on the southeast. Farther eastward in this part of Europe the mountains seem to have been too low to have furnished centres for any general dispersion of glacial ice.

Upon the south side of the Alps the ancient glaciers spread far out upon the plains of Lombardy, where moraines of vast extent and of every description enable the student to determine the exact limits of the ancient ice-action. From the southern flanks of Mont Blanc and Monte Rosa, and from the snow-fields of the western Alps, glaciers of great volume descended into the valley of Dora Baltea (vale of Aosta), and on emerging from the mountain valley Spread Out over the plains around Ivrea, leaving moraine hills in some instances 1,500 feet in height. The total length of this glacier was as much as one hundred and twenty miles. From the snow-fields in the vicinity of Mont Cenis, also, glaciers extended down the Dora Ripera to the vicinity of Turin, and down other valleys to a less extent. The lateral moraines of the Diore, on the south side of Mont Blanc, at the head of the Dora Baltea, are 2,000 feet above the present river, and extend upon the left bank for a distance of twenty miles.

From the eastern Alps, glaciers descended through all the valleys of the Italian lakes and deposited vast terminal moraines, which still obstruct the drainage, and produce the charming lakes of that region. A special historic interest pertains to the series of concentric moraines south of Lake Garda, since it was in the reticulations of this glacial deposit that the last great battle for Italian liberty was fought on June 24, 1859. Defeated in the engagements farther up the valley of the Po, the Austrian general Benedek took his final stand to resist the united forces of France and Italy behind an outer semicircle of the moraine hills south of this lake (some of which are 500 or 600 feet above the surrounding country), with his centre at Solferino, about ten miles from Peschera. Here, behind this natural fortification, he awaited the enemy, who was compelled to perform his manoeuvres on the open plain which spread out on every side. But the natural fortifications furnished by the moraine hills were too extensive to be defended by an army of moderate size. The troops of Napoleon and Victor Immanuel concentrated at Solferino and broke through the line. Thus the day was lost to the Austrians, and they retired from Lombardy, leaving to Italy both the artificial and the natural fortifications that guard the southern end of this important entrance to the Tyrolese Alps. When once his attention is called to the subject, the traveller upon the railroad cannot fail to notice this series of moraines, as he enters it through a tunnel at Lonato on the west, and emerges from it at Soma Campagna, eighteen or twenty miles distant to the east. A monument celebrating the victory stands upon a moraine hill about half-way between, at Martino della Battaglie.

In other portions of central and southern Europe the mountains were too low to furnish important centres for glacial movements. Still, to a limited extent, the signs of ancient glaciers are seen in the mountains of the Black Forest, in the Harz and Erzgebirge, and in the Carpathians on the east and among the Apennines on the south. In Spain, also, there were limited ice-fields on the higher portions of the Sierra Nevada and in the mountains of Estremadura, and perhaps in some other places. In France, small glaciers were to be found in the higher portions of the Auvergne, of the Morvan, of the Vosges, and of the Cevennes; while, from the Pyrenees, glaciers extended northward throughout nearly their whole extent. The ice-stream descending from the central mass of Maladetta through the upper valley of the Garonne, was joined by several tributaries, and attained a length of about forty-five miles.

The British Isles.

During the climax of the Glacial period the Hebrides to the north of Scotland were covered with ice to a depth of 1,600 feet. How far westward of this it moved out to the sea, it is of course impossible to tell. But in the channels between the Hebrides and Scotland it is evident that the water was completely expelled by the ice, and that, from a height of 1,600 feet above the Hebrides to the northern shores of Scotland, there was a continuous ice-field sloping southward at the rate of about twenty-five feet a mile.

Scotland itself was completely enveloped in glacial ice. Prevented by the Scandinavian Glacier from moving eastward, the Scotch movement was compelled to be westward and southward. On the southwest the ice-stream reached the shores of Ireland, and became confluent with the glaciers that enveloped that island, completely filling the Irish Sea.

There are so many controverted points respecting the glacial geology of England, and they have such an important bearing upon the main question of this volume, that a pretty full discussion of them will be necessary. I have recently been over enough of the ground myself to become satisfied of the general correctness of the views entertained by my late colleague, the lamented Professor Henry Carvill Lewis, whose death in 1888 took place before the publication of his most mature conclusions. But the lines of investigation to which he gave so powerful an impulse have since been followed out by an active body of scientific observers. To give the statement of facts greater precision and authority, I have committed the preparation of it to the Secretary of the Northwest of England Boulder Committee, Percy F. Kendall, F. G. S., Lecturer on Geology at the Yorkshire College, Leeds, and at the Stockport Technical School, England.

"All the characteristic evidences of the action of land-ice can be found in the greatest perfection in many parts of England and Wales. Drumlins, kames, roches moutonnées, far-travelled erratics, terminal moraines, and perched blocks, all occur. There are, besides, in the wide-spread deposits of boulder-clay which cover so many thousands of square miles on the low grounds lying on either side of the Pennine chain, evidences of the operation of ice-masses of a size far exceeding that of the grandest of existing European glaciers. But, while the proofs of protracted and severe glaciation are thus patent, there are, nevertheless, many apparently anomalous circumstances which arrest the attention when the whole country is surveyed. The glacial phenomena appear to be strictly limited to the country lying to the northward of a line extending from the Bristol Channel to the mouth of the Thames; and within the glaciated area there are many extensive tracts of land devoid of 'drift' or other indications of ice-action.

"By comparison with the phenomena displayed in the North American continent, English glacial geology must seem puny and insignificant; but, just as with the features of the 'Solid Geology,' we have compressed within the narrow limits of our isles an epitome of the features which across the Atlantic require a continent for their exposition. It has resulted from this concentration that English geology requires a much closer and more minute investigation. And the difficulty which has been experienced by glacial geologists of dealing with an involved series of facts has, in the absence of any clue leading to the co-ordination of a vast series of more or less disconnected observations, resulted in the adoption, to meet certain local anomalies, of explanations which were very difficult if not impossible of reconciliation with facts observed in adjacent areas. Thus, to account for shell-bearing drift extending up to the water-shed on one side of a lofty range of hills, a submergence of the land to a depth of 1,400 feet has been postulated; leaving for independent explanation the fact, that the opposite slopes of the hills and the low ground beyond were absolutely destitute of drift or of any evidence of marine action.

"In the following pages I must adopt a somewhat dogmatic tone, in order to confine myself within the limits of space which are imposed; and trust rather to the cohesion and consistency of the explanations offered and to a few pregnant facts than to the weighing and contrasting of rival theories.

"The facts point conclusively to the action in the British Isles of a series of glaciers radiating outward from the great hill chains or clusters, and, as the refrigeration progressed, becoming confluent and moving though in the same general direction, yet with less regard to the minor inequalities of the ground. During these two stages many glaciers must have debouched upon the sea-coast, with the consequent production of icebergs, which floated off with loads of boulders and dispersed them in the random fashion which is a necessary characteristic of transport by floating ice.

"With a further accentuation of the cold conditions the discharge of bergs from terminal fronts which advanced into the extremely shallow seas surrounding the British shores would be quite inadequate to relieve the great press of ice, and a further coalescence of separate elements must have resulted. In the case of enclosed seas--as, for example, the Irish Sea--the continued inthrust of glacier-ice would expel the water completely; and the conjoined ice-masses would take a direction of flow the resultant of the momentum and direction of the constituent elements. In other cases--as, for example, in the North Sea--extraneous ice approaching the shores might cause a deflection of the flow of the native glaciers, even though the foreign ice might never actually reach the shore.

"To such a system of confluent glaciers, and to the separate elements out of which they grew, and into which, after the culmination, they were resolved, I attribute the whole of the phenomena of the English and Welsh drift. And only at one or two points upon the coast, and raised but little above the sea-level, can I recognise any signs of marine action.

"The Preglacial Level of the Land.--There is very little direct evidence bearing upon this point. In Norfolk the famous forest bed, with its associated deposits, stands at almost precisely the level which it occupied in preglacial times. At Sewerby, near Flamborough Head, there is an ancient beach and 'buried cliff' which the sea is now denuding of its swathing of drift-deposits, and its level can be seen to be almost absolutely coincident with the present beach. Mr. Lamplugh, whose description of the 'Drifts of Flamborough Head,' constitutes one of the gems of glacial literature, considers that there is clear evidence that the land stood at this level for a long period. The beach is covered by a rain-wash of small extent, and that in turn by an ancient deposit of blown sand, while the lowest member of the drift series of Yorkshire covers the whole. Mr. Lamplugh thinks that the blown sand may indicate a slight elevation of the land; but the beach appears to me to be the storm beach, and the reduction in the force of the waves such as would result from the approach of an ice-front a few miles to the seaward would probably produce the necessary conditions.

"Six miles to the northward of Flamborough, at Speeton, a bed of estuarine silt containing the remains of mollusca in the position of life occurs at an altitude of ninety feet above high-water mark. Mr. Lamplugh inclines to the opinion that this bed is of earlier date than the 'buried cliff'; he also admits the possibility that its superior altitude may be due to a purely local upward bulging of the soft Lower Cretaceous clays upon which the estuarine bed rests by the weight of the adjacent lofty chalk escarpment.

"The evidence obtained from inland sections and borings in different parts of England has been taken to indicate a greater altitude in preglacial times. Thus, in Essex, deep-borings have revealed the existence of deep drift-filled valleys, having their floors below sea-level. The valley of the Mersey is a still better example. Numerous borings have been made in the neighbourhood of Widnes and at other places in the lower reaches of the river, making it clear that there is a channel filled with drift and extending to 146 feet below mean sea-level. This, with several other instances, has been taken to indicate a greater altitude for the land in preglacial times, since a river could not erode its channel to such a depth below sea-level. The argument appears inconclusive for one principal reason: no mention is made of any river gravels or other alluvium in the borings. Indeed, there is an explicit statement that the deposits are all glacial, showing that the channel must have been cleared out by ice. This, therefore, leaves open the vital question, whether the deposits removed were marine or fluviatile. It may be remarked that the great estuary of the Mersey has undoubtedly been produced by a post-glacial (and probably post-Roman) movement of depression.

"The Preglacial Climate.--In all speculations regarding the cause of the Glacial epoch, due account must be taken of the undoubted fact that it came on with extreme slowness and departed with comparative suddenness. In the east of England an almost perfect and uninterrupted sequence of deposits is preserved, extending from the early part of the Pliocene period down to the present day.

"These in descending order are:

"1. Post-glacial sands, gravels, etc.

"2. Glacial series.

"3. The 'Forest Bed' and associated marine deposits.

"4. Chillesford clay and sand.

"5. The many successive stages of the Red Crag. (The Norwich Crag is a local variation of the upper part of the Red Crag.)

"6. The Coralline Crag.

"The fossils preserved in these deposits, apart from the physical indications, exhibit the climatal changes which accompanied their deposition. The Coralline Crag contains a fauna consisting mainly of species which now range to the Mediterranean, many of them being restricted to the warm southern waters. Associated with these are a few boreal forms, but they are represented in general by few individuals. Here and there in the deposits of this age far-travelled stones are to be found, but they are always accounted great rarities.

"The Red Crag consists of an irregular assemblage of beaches and sand-banks of widely different ages, but their sequence can be made out with ease by a study of the fauna. In the oldest deposits, Mediterranean species are very numerous, while the boreal forms are comparatively rare; but in successive later deposits the proportions are very gradually reversed, and from the overlying Chillesford series the Mediterranean species are practically absent. The physical indications run pari passu with the paleontological, and in the newer beds of the Red Crag far-travelled stones are common.

"In the Forest Bed series there is a marine band--the Leda myalis bed--which contains an almost arctic assemblage of shells; while at about the same horizon plant remains have been found, including such high northern species as Salix polaris and Betula nana.

"The glacial deposits do not, in my opinion, contain anywhere in England or Wales a genuine intrinsic fauna, such shells as occur in the East Anglian glacial deposits having been derived in part from a contemporary sea-bed, and, for the rest, from the older formations, down perhaps to the Coralline Crag. In the post-glacial deposits we have hardly any trace of a survival of the boreal forms, and I consider that the whole marine fauna of the North Sea was entirely obliterated at the culmination of the Glacial epoch, and that the repeopling in post-glacial times proceeded mainly from the English Channel, into which the northern forms never penetrated.

"The Great Glacial Centres.

"Where such complex interactions have to be described as were produced by the conflicting glaciers of the British Isles it is difficult to deal consecutively with the phenomena of any one area, but with short digressions in explanation of special points it may be possible to accomplish a clear presentation of the facts.

"Wales.--The phenomena of South Wales are comparatively simple. Great glaciers travelled due southward from the lofty Brecknock Beacons, and left the characteristic moutonnée appearance upon the rocky bed over which they moved. The boulder-transport is in entire agreement with the other indications, and there are no shells in the drift. The facts awaiting explanation are the occurrence in the boulder-clays of Glamorganshire, at altitudes up to four hundred feet, of flints, and of igneous rocks somewhat resembling those of the Archæan series of the Wrekin. At Clun, in Shropshire, a train of erratics (see map) has been traced back to its source to the westward. On the west coast, in Cardigan Bay, the boulders are all such as might have been derived from the interior of Wales. At St. David's Peninsula, Pembrokeshire, striæ occur coming in from the northwest, and, taken with the discovery of boulders of northern rocks, may point to a southward extension of a great glacier produced by confluent sheets that choked the Irish Sea. Information is very scanty regarding large areas in mid-Wales, but such as can be gathered seems to point to ice-shedding having taken place from a north and south parting line. In North Wales, much admirable work has been done which clearly indicates the neighbourhood of Great Arenig (Arenig Mawr) as the radiant point for a great dispersal of blocks of volcanic rock of a characteristic Welsh type.

"Ireland.--A brief reference must be made to Ireland, as the ice which took origin there played an important part in bringing about some strange effects in English glaciation, which would be inexplicable without a recognition of the causes in operation across the Irish Sea. Ireland is a great basin, surrounded by an almost continuous girdle of hills. The rainfall is excessive, and the snow-fall was probably more than proportionately great; therefore we might expect that an ice-sheet of very large dimensions would result from this combination of favouring conditions. The Irish ice-sheet appears to have moved outward from about the centre of the island, but the main flow was probably concentrated through the gaps in the encircling mountains.

"Galloway.--The great range of granite mountains in the southwestern corner of Scotland seems to have given origin to an immense mass of ice which moved in the main to the southward, and there are good grounds for the belief that the whole ice-drainage of the area, even that which gathered on the northern side of the water-shed, ultimately found its way into the Irish Sea basin and came down coastwise and across the low grounds of the Rinns of Galloway, being pushed down by the press of Highland ice which entered the Firth of Clyde. It is a noteworthy fact that marine shells occur in the drift in the course taken by the ice coming on to the extremity of Galloway from the Clyde.

"The Lake District.--A radial flow of ice took place down the valleys from about the centre of the Cumbrian hill-plexus, but movement to the eastward was at first forbidden by the great rampart of the Cross Fell escarpment, which stretches like a wall along the eastern side of the Vale of Eden.

"During the time when the Cumbrian glaciers had unobstructed access to the Solway Frith, to the Irish Sea, and to Morecambe Bay, the dispersal of boulders of characteristic local rocks would follow the ordinary drainage-lines; but, as will be shown later, a state of affairs supervened in the Irish Sea which resulted, in many cases, in a complete reversal of the ice-flow.

"The Pennine Chain was the source of glaciers of majestic dimensions upon both its flanks in the region north of Skipton, but to the southward of that breach in the chain (see map) no evidence is obtainable of any local glaciers.

"The Confluent Glaciers.

"With the growth of ice-caps upon the great centres a condition of affairs was brought about in the Irish Sea productive of results which will readily be foreseen. The enormous volumes of ice poured into the shallow sea from north, south, east, and west, resulted in such a congestion as to necessitate the initiation of some new systems of drainage.

"The Irish Sea Glacier.--The ice from Galloway, Cumbria, and Ireland became confluent, forming what the late Professor Carvill Lewis termed 'the Irish Sea Glacier,' and took a direction to the southward. Here it came in diametrical conflict with the northward-flowing element of the Welsh sheet, which it arrested and mastered; and the Irish Sea Glacier bifurcated, probably close upon the precipitous Welsh coast to the eastward of the Little Orme's Head, and the two branches flowed coastwise to eastward and westward, keeping near the shore-line.

"The westerly branch swept round close to the coast in a southwesterly direction, and completely overrode Anglesea; striating the rock-surfaces from northeast to southwest (see map), and strewing the country with its bottom-moraine, containing characteristic northern rocks, such as the Galloway granites, the lavas and granites of the central and western portions of the Lake District, and fragments of shells derived from shell-banks in the Irish Sea. One episode of this phase of the ice-movement was the invasion of the first line of hills between the Menai Straits and Snowdon. The gravels and sands of Fridd-bryn-mawr, Moel Tryfaen, and Moel-y-Cilgwyn, are the coarser washings of the bottom-moraine, and consequently contain such rock-fragments and shells as characterise it. From Moel-y-Cilgwyn southward, evidence is lacking regarding the course taken by the glacier, but it probably passed over or between the Rivals Mountains (Yr Eifl), and down Cardigan Bay at some distance from the coast in confluence with the ice from mid-Wales; and, as I have suggested, may have passed over St. David's Head.

"Returning now towards the head of the glacier we may follow with advantage its left bank downward. The ice-flow on the Cumberland coast appears to have resembled very much that in North Wales. A great press of ice from the northward (Galloway) seems to have had a powerful 'easting' imparted to it by the conjoint influences of the thrust of the Irish ice and the inflow of ice from the Clyde. Whatever may have been the cause, the effect is clear: about Ravenglass cleavage took place, and a flow to northward and to southward, each bending easterly. By far the larger mass took a southerly course and bent round Black Combe, over Walney, and a strip of the mainland about Barrow in Furness, and out into and across Morecambe Bay. Its limits are marked in the field by the occurrence of the same rocks which characterise it in Anglesea, viz., the granites of Galloway and of west and central Cumbria.

"The continued thrust shouldered in the glacier upon the mainland of Lancashire, but the precise point of emergence has not yet been traced, though it cannot be more than a few miles from the position indicated on the map. I should here remark, that all along the boundaries the Irish Sea Glacier was confluent with local ice, except, probably, in that part of the Pennine chain to the southward of Skipton. Down to Skipton there was a great mass of Pennine ice which was compelled to take an almost due southerly course, and thus to run directly athwart the direction of the main hills and valleys. A sharp easterly inflection of the Irish Sea Glacier carried it up the valley of the Ribble, and thence, under the shoulder of Pendle, to Burnley, where Scottish granites are found in the boulder-clay.

"On the summit of the Pennine water-shed, at Heald Moor, near Todmorden (1,419 feet), boulder-clay has been found containing erratics belonging to this dispersion; while in the gorge of the Yorkshire Calder, which flows along the eastern side of the same hill, not a vestige of such a deposit is to be found, saving a few erratic pebbles at a distance of eight or ten miles, which were probably carried down by flood-wash from the edge of the ice.

"From this point the limits of the ice may be traced along the flanks of the Pennine chain at an average altitude of about 1,100 feet.

"At one place the erratics can be traced to a position which would indicate the formation of an extra-morainic lake having its head at a col about 1,000 feet above sea-level, separating it from the valley of an eastward-flowing stream, the Wye, about twelve miles down which a few granite blocks have been found. Other extra-morainic lakes must have been formed, but very little information has been collected regarding them. The Irish Sea Glacier can be shown to have spread across the whole country to the westward of the line I have traced, and beyond the estuary of the Dee.

"I may now follow its boundaries on the Welsh coast, and pursue the line to the final melting-place of the glacier. From the Little Orme's Head the line of confluence with the native ice is pretty clearly defined. It runs in, perhaps, half a mile from the shore, until the broad low tract of the Vale of Clwyd is reached. Here the northern ice obtained a more complete mastery, and pushed in even as far as Denbigh. This extreme limit was probably attained as a mere temporary episode. Horizontal striæ on a vertical face of limestone on the crags dominating the mouth of the vale on the eastern side attest beyond dispute the action of a mass of land-ice moving in from the north.

"I may here remark, that in this district the deposits furnish a very complete record of the events of the Glacial period. In the cliffs on the eastern side of the Little Orme's Head, and at several other points along the coast towards the east, a sequence may be observed as follows:

"4. Boulder-clay with northern erratics and shells.

"3. Sands and gravels with northern erratics and shells.

"2. Boulder-clay with northern erratics and shells.

"1. Boulder-clay with Welsh erratics and no shells.

"A similar succession is to be seen in the Vale of Clwyd. The interpretation is clear: In the early stages of glaciation the Welsh ice spread without hindrance to, and laid down, bed No. 1; then the northern ice came down, bringing its typical erratics and the scourings of the sea-bottom, and laid down the variable series of clays, sands, and gravels which constitute Nos. 2, 3, and 4 of the section.

"In the Vale of Clwyd an additional interest is imparted to the study of the drift from the circumstance that the remains of man have been found in deposits in caves sealed with drift-beds. The best example is the Cae Gwyn caves, in which flint implements and the bones and teeth of various extinct animals were found embedded in 'cave-earth' which was overlaid by bedded deposits of shell-bearing drift, with erratics of the northern type.

"It has been supposed that the drift-deposits were marine accumulations; but it is inconceivable that the cave could ever have been subjected to wave-action without the complete scouring out of its contents.

"To resume the delineation of the limits of the great Irish Sea Glacier: From the Vale of Clwyd the boundary runs along the range of hills parallel to the estuary of the Dee at an altitude of about nine hundred feet. As it is traced to the southeast it gradually rises, until at Frondeg, a few miles to the northward of the embouchure of the Yale of Llangollen, it is at a height of 1,450 feet above sea-level. Thence it falls to 1,150 feet at Gloppa, three miles to the westward of Oswestry, and this is the most southerly point to which it has been definitely traced on the Welsh border, though scattered boulders of northern rocks are known to occur at Church Stretton.

"Along the line from the Vale of Clwyd to Oswestry the boundary is marked by a very striking series of moraine-mounds. They occur on the extreme summits of lofty hills in a country generally almost driftless, and their appearance is so unusual that one--Moel-y-crio--at least has been mistaken for an artificial tumulus. The limitation of the dispersal of northern erratics by these mounds is very clear and sharp; and Mackintosh, in describing those at Frondeg, remarked that, while no northern rocks extended to the westward of them, so no Welsh erratics could be found to cross the line to the eastward. There are Welsh erratics in the low grounds of Cheshire and Shropshire, but their distribution is sporadic, and will be explained in a subsequent section.

"Having thus followed around the edges of this glacier, it remains to describe its termination. It is clear that the ice must have forced its way over the low water-shed between the respective basins of the Dee and the Severn. So soon as this ridge (less than 500 feet above the sea) is crossed, we find the deposits laid down by the glacier change their character, and sands and gravels attain a great predominance. Near Bridgenorth, and, at other places, hills composed of such materials attain an altitude of 200 feet. From Shrewsbury via Burton, and thence, in a semicircular sweep, through Bridgenorth and Enville, there is an immense concentration of boulders and pebbles, such as to justify the designation of a terminal moraine. To the southward, down the valley of the Severn, existing information points to the occurrence merely of such scattered pebbles as might have been carried down by floods. In the district lying outside this moraine there is a most interesting series of glacial deposits and of boulders of an entirely different character. (See map.)

"From the neighbourhood of Lichfield, through some of the suburbs of Birmingham, and over Frankley Hill and the Lickey Hills to Bromsgrove, there is a great accumulation of Welsh erratics, from the neighbourhood, probably, of Arenig Mawr.

"The late Professor Carvill Lewis suggested that these Arenig rocks might have been derived from some adjacent outcrop of Palæozoic rocks--a suggestion having its justification in the discoveries that had been made of Cumbrian rocks in the Midlands. To test the matter, an excavation was made at a point selected on Frankley Hill, and a genuine boulder-clay was found, containing erratics of the same type as those found upon the surface.

"The explanation has since been offered that this boulder-clay was a marine deposit laid down during a period of submerge nee. Apart from the difficulty that the boulder-clay displays none of the ordinary characteristics of a marine deposition, but possesses a structure, or rather absence of structure, in many respects quite inconsistent with such an origin, and contains no shells or other remains of marine creatures, it must be pointed out that no theory of marine notation will explain the distribution of the erratics, and especially their concentration in such numbers at a station sixty or seventy miles from their source.

"Upon the land-ice hypothesis this difficulty disappears. During the early stages of the Glacial period the Welsh ice had the whole of the Severn Valley at its mercy, and a great glacier was thrust down from Arenig, or some other point in central Wales, having an initial direction, broadly speaking, from west to east. This glacier extended across the valley of the Severn, sweeping past the Wrekin, whence it carried blocks of the very characteristic rocks to be lodged as boulders near Lichfield; and it probably formed its terminal moraine along the line indicated. (See lozenge-shaped marks on the map.) As the ice in the north gathered volume it produced the great Irish Sea Glacier, which pressed inland and down the Vale of Severn in the manner I have described, and brushed the relatively small Welsh stream out of its path, and laid down its own terminal moraine in the space between the Welsh border and the Lickey Hills. It seems probable that the Welsh stream came mainly down the Vale of Llangollen, and thence to the Lickey Hills. Boulders of Welsh rocks occur in the intervening tract by ones and twos, with occasional large clusters, the preservation of any more connected trail being rendered impossible by the great discharge of water from the front of the Irish Sea Glacier, and the distributing action of the glacier itself.

"Within the area in England and Wales covered by the Irish Sea Glacier all the phenomena point to the action of land-ice, with the inevitable concomitants of subglacial streams, extra-morainic lakes, etc. There is nothing to suggest marine conditions in any form except the occurrence of shells or shell fragments; and these present so many features of association, condition, and position inconsistent with, what we should be led to expect from a study of recent marine life, that conchologists are unanimous in declaring that not one single group of them is on the site whereon the shells lived. It is a most significant fact--one out of a hundred which could be cited did space permit--that in the ten thousand square miles of, as it is supposed, recently elevated sea-bottom, not a single example of a bivalve shell with its valves in apposition has ever been found! Nor has a boulder or other stone been found encrusted with those ubiquitous marine parasites, the barnacles.

"The evidences of the action of land-ice within the area are everywhere apparent in the constancy of direction of-- (1.) Striæ upon rock surfaces. (2.) The terminal curvature of rocks. (3.) The 'pull-over' of soft rocks. (4.) The transportal of local boulders. (5.) The orientation of the long axes of large boulders. (6.) The false bedding of sands and gravels. (7.) The elongation of drift-hills. (8.) The relations of 'crag and tail.' There is a similar general constancy, too, in the directions of the striæ upon large boulders. Upon the under side they run longitudinally from southeast (or thereabouts) to northwest, while upon the upper surface they originate at the opposite end, showing that the scratches on the under side were produced by the stone being dragged from northwest to southeast, while those on the top were the product of the passage of stone-laden ice over it in the same direction.

"Such an agreement cannot be fortuitous, but must be attributed to the operation of some agent acting in close parallelism over the whole area. To attribute such regularity to the action of marine currents is to ignore the most elementary principles of marine hydrology. Icebergs must, in the nature of things, be the most erratic of all agents, for the direction of drift is determined--among other varying factors--by the draught of the berg. A mass of small draught will be carried by surface currents, while one of greater depth will be brought within the influence of under-currents; and hence it not infrequently happens that while floe-ice is drifting, say, to the southeast, giant bergs will go crashing through it to the northwest. There are tidal influences also to be reckoned with, and it is matter of common knowledge that flotsam and jetsam travel back and forth, as they are alternately affected by ebb and flood tide.

"Bearing these facts in mind, it is surely too much to expect that marine ice should transport boulders (how it picked up many of them also requires explanation) with such unfailing regularity that it can be said without challenge, 'boulders in this district [South Lancashire and Cheshire] never occur to the north or west of the parent rock.' The same rule applies without a single authentic exception to the whole area covered by the eastern branch of the Irish Sea Glacier; and hence it comes about that not a single boulder of Welsh rock has ever been recorded from Lancashire.

"The Solway Glacier.--The pressure which forced much of the Irish Sea ice against the Cumbrian coast-line caused, as has been described, a cleavage of the flow near Ravenglass, and, having followed the southerly branch to its termination in the midlands, the remaining moiety demands attention.

"The 'easting' motion carried it up the Solway Frith, its right flank spreading over the low plain of northern Cumberland, which it strewed with boulders of the well-known 'syenite' (granophyre) of Buttermere. When this ice reached the foot of the Cross Fell escarpment, it suffered a second bifurcation, one branch pushing to the eastward up the valley of the Irthing and over into Tyneside, and the other turning nearly due southward and forcing its way up the broad Vale of Eden.

"Under the pressure of an enormous head of ice, this stream rose from sea-level, turned back or incorporated the native Cumbrian Glacier which stood in its path, and, having arrived almost at the water-shed between the northern and the southern drainage, it swept round to the eastward and crossed over the Pennine water-shed; not, however, by the lowest pass, which is only some 1,400 feet above sea-level, but by the higher pass of Stainmoor, at altitudes ranging from 1,800 to 2,000 feet. The lower part of the course of this ice-flow is sufficiently well characterised by boulders of the granite of the neighbourhood of Dalbeattie in Galloway; but on its way up the Vale of Eden it gathered several very remarkable rocks and posted them as way-stones to mark its course. One of these rocks, the Permian Brockram, occurs nowhere in situ at altitudes exceeding 700 feet, yet in the course of its short transit it was lifted about a thousand feet above its source. The Shap granite (see radiant point on map) is on the northern side of the east and west water-sheds of the Lake District, and reaches its extreme elevation, (1,656 feet) on Wasdale Pike; yet boulders of it were carried over Stainmoor, at an altitude of 1,800 feet literally by tens of thousands.

"This Stainmoor Glacier passed directly over the Pennine chain, past the mouths of several valleys, and into Teesdale, which it descended and spread out in the low grounds beyond. Pursuing its easterly course, it abutted upon the lofty Cleveland Hills and separated into two streams, one of which went straight out to sea at Hartlepool, while the other turned to the southward and flowed down the Vale of York, being augmented on its way by tributary glaciers coming down Wensleydale. The final melting seems to have taken place somewhere a little to the southward of York; but boulders of Shap granite by which its extension is characterised have been found as far to the southward as Royston, near Barnsley.

"The other branch of the Solway Glacier--that which travelled due eastward--passed up the valley of the Irthing, and over into that of the Tyne, and out to sea at Tynemouth. It carried the Scottish granites with it, and tributary masses joined on either hand, bringing characteristic boulders with them.

"The fate of those elements of the Solway Frith Glacier which reached the sea is not left entirely to conjecture. The striated surfaces near the coast of Northumberland indicate a coastwise flow of ice from the northward--probably from the Frith of Forth--and the glaciers coming out from the Tyne and Tees were deflected to the southward.

"There is conclusive evidence that this ice rasped the cliffs of the Yorkshire coast and pressed up into some of the valleys. Where it passed the mouth of the Tees near Whitby it must have had a height of at least 800 feet, but farther down the coast it diminished in thickness. It nowhere extended inland more than a mile or two, and for the most part kept strictly to the coast-line. Along the whole coast are scattered erratics derived from Galloway and the places lying in the paths of the glaciers. In many places the cliffs exhibit signs of rough usage, the rocks being crumpled and distorted by the violent impact of the ice. At Filey Brigg a well-scratched surface has been discovered, the striation being from a few degrees east of north.

"At Speeton the evidence of ice-sheet or glacier-work is of the most striking character. On the top of the cliffs of Cretaceous strata a line of moraine-hills has been laid down, extending in wonderful perfection for a distance of six miles. They consist of a mixture of sand, gravel, and a species of clay-rubble, with occasional masses of true boulder-clay, the whole showing the arched bedding so characteristic of such accumulations. At the northerly end the moraine keeps close to the edge of the chalk cliffs, which are there 400 feet high, and the hills are frequently displayed in section; but as the elevation of the cliffs declines they fall back from the edge of the cliffs and run quite across the headland of Flamborough, and are again exposed in section in Bridlington Bay. One remarkable and significant fact is pointed out, namely, that behind this moraine, within half a mile and at a lower level, the country is almost absolutely devoid of any drift whatever.

"The interpretation of these phenomena is as follows: When the valley-glaciers reached the sea they suffered the deflection which has been mentioned, partly as the result of the interference of ice from the east of Scotland, but also influenced directly by the cause which operated upon the Scottish ice and gave direction to it--that is, the impact of a great glacier from Scandinavia, which almost filled the North Sea, and turned in the eastward-flowing ice upon the British coast.

"It is easy to see how this pressure must have forced the glacier-ice against the Yorkshire coast, but vertical chalk cliffs 400 feet in height are not readily surmounted by ice of any thickness, however great, and so it coasted along and discharged its lateral moraine upon the cliff-tops. As the cliffs diminished in height we find the moraine farther inland, and, as I have pointed out, the ice completely overrode Flamborough Head. Amongst the boulders at Flamborough are many of Shap granite, a few Galloway granites, a profusion of Carboniferous rocks, brought by the Tyne branch of the Sol way Glacier as well as by that of Stainmoor, and, besides many torn from the cliffs of Yorkshire, a few examples of unquestionable Scandinavian rocks, such as the well-known Rhomben-porphyr. It is important to note that about ten to twenty miles from the Yorkshire coast there is a tract of sea-bottom called by trawlers 'the rough ground,' in allusion to the fact that it is strewn with large boulders, amongst which are many of Shap granite. This probably represents a moraine of the Teesdale Glacier, laid down at a time when the Scandinavian Glacier was not at its greatest development.

"On the south side of Flamborough Head the 'buried cliff' previously alluded to occurs. The configuration of the country shows--and the conclusion is established by numerous deep-borings--that the preglacial coast-line takes a great sweep inland from here, and that the plain of Holderness is the result of the banking-up of an immense thickness of glacial débris. In the whole country reviewed, from Tynemouth to Bridlington, wherever the ice came on to the land from the seaward, it brought in shells and fragmentary patches of the sea-bottom involved in its ground moraine. Space does not permit of a detailed description of the several members of the Yorkshire Drift, and I pass on to deal in a general way with the glacial phenomena of the eastern side of England.

"The East Anglian Glacier.--The influence of the Scandinavian ice is clearly seen in the fact that the entire ice-movement down the east coast south of Bridlington was all from the seaward. Clays, sands, and gravels, the products of a continuous mass of land-ice coming from the northeast are spread over the whole country, from the Trent to the high grounds on the north of London overlooking the Thames.

"The line of extreme extension of these drift-deposits runs from Finchley (near London), in the south across Hertfordshire, through Cambridgeshire, with outlying patches at Gogmagog and near Buckingham, and northwestward over a large portion of Leicestershire into the upper waters of the Trent, embracing the elevated region of Palæozoic rocks at Charnwood Forest, near Leicester.

"Reserving the consideration of the very involved questions connected with the drifts of the upper part of the Trent Valley, I may pass on to join the phenomena of the southeastern counties with those at Flamborough Head. From Nottinghamshire the limits of the drift of the East Anglian Glacier seem to run in a direction nearly due west to east, for the great oolitic escarpment upon which Lincoln Cathedral is built is absolutely driftless to the northward of the breach about Sleaford. However, along the western flank of the oolitic range true boulder-clay occurs, bordering and doubtless underlying the great fen-tract of mid-Lincolnshire; and the great Lincolnshire Wolds appear to have been completely whelmed beneath the ice.

"The most remarkable of the deposits in this area is the Great Chalky Boulder-Clay, which consists of clay containing much ground-up chalk, and literally packed with well-striated boulders of chalk of all sizes, from minute pebbles up to blocks a foot or more in diameter. Associated with them are boulders of various foreign rocks, and many flints in a remarkably fresh condition, and still retaining the characteristic white coat, except where partially removed by glacial attrition.

"One of the perplexing features of the glacial phenomena in the eastern counties of England is the extension of true chalky boulder-clay to the north London heights at Finchley and elsewhere; for only the faintest traces are to be found in the gravel deposits of the Thames Valley of any wash from such a deposit, or from a glacier carrying such materials.

"It has been suggested that the deposit may have been laid down in an extra-morainic lake, or in an extension of the North. Sea, but these suggestions leave the difficulty just where it was. If a lake or sea could exist without shores, a glacier-stream might equally dispense with banks. Within the area of glaciation, defined above, abundant evidence of the action of land-ice is obtainable, though striated surfaces are extremely rare--a fact attributable to the softness of the chalk and clays which occupy almost the whole area. Well-striated surfaces are found on the harder rocks, as, for example, on the oolitic limestone at Dunston, near Lincoln.

"Mr. Skertchly has remarked that the proofs of the action of land-ice are irrefragable. The Great Chalky Boulder-Clay covers an area of 3,000 square miles, and attains an altitude of 500 feet above the sea-level, thus bespeaking, if the product of icebergs, 'an extensive gathering-ground of chalk, having an elevation of more than 500 feet. But where is it? Certainly not in Western Europe, for the chalk does not attain so great an elevation except in a few isolated spots.'

"It has been further pointed out by Mr. Skertchly, that the condition of the flints in this deposit furnishes strong evidence that they could not have been carried by floating ice nor upon a glacier, for, in either of the latter events, there must have been some exposure to the weather, which, as he remarks, would have rendered them worthless to the makers of gun-flints, whereas they are now regularly collected for their use.

"The way in which the boulder-clay is related to the rocks upon which it rests is a conclusive condemnation of any theory of floating ice; for example, where it rests upon Oxford Clay, it contains the fossils characteristic of that formation, as it is largely made up of the clay itself. The exceptions to this rule are as suggestive as those cases which conform to it. Each outcrop yields material to the boulder-clay to the south westward, showing a pull-over from the northeast.

"One of the most remarkable features of the drift of this part of England is the inclusion of gigantic masses of rock transported for a short distance from their native outcrop, very often with so small a disturbance that they have been mapped as in situ. Examples of chalk-masses 800 feet in length, and of considerable breadth and thickness, have been observed in the cliffs near Cromer, in Norfolk, but they are by no means restricted to situations near the coast. One example is mentioned in which quarrying operations had been carried on for some years before any suspicion was aroused that it was merely an erratic. The huge boulders were probably dislodged from the parent rock by the thrust of a great glacier, which first crumbled the beds, then sheared off a prominent fold and carried it along. This explanation we owe to Mr. Clement Reid. The drift-deposits of this region frequently contain shells, but they rarely constitute what may be termed a consistent fauna, usually showing such an association as could only be found where some agent had been at work gathering together shells of different habitats and geological age.

"If the ice-sheet, instead of flowing over the beds, happens to plough into them or abut against them, it would bend up a boss of chalk, as at Beeston. A more extensive disturbance, like that at Trimingham drives before it a long ridge of the bads, and nips up the chalk, till, like a cloth creased by the sliding of a heavy book, it is folded into an inverted anticlinal. A slight increase of pressure, and the third stage is reached--the top of the anticlinal being entirely sheared off, the chalk boulder driven up an incline, and forced into the overlying boulder-clays." (Clement Reid.)]

"Attempts have been made to correlate the deposits over the whole area, but with very indifferent success. A consideration of the consequences of the invasion of the country by an ice-stream from the northeast will prepare us for any conceivable complication of the deposits.

"The main movement was against the drainage of the country, so that the ice-front must have been frequently in water. There would be aqueous deposition and erosion; the kneading up of morainic matter into ground-moraine; irregularities of distribution and deposition due to ice floating in an extra-morainic lake; flood-washes at different points of overflow; and other confusing causes, which make it rather matter for surprise that any order whatever is traceable.

"I now turn to the valley of the Trent. We find that it occupies such a position that it would be exposed, successively or simultaneously, to the action of ice-streams of most diverse origin. I have shown that the area to the westward of Lichfield was invaded at one period by a Welsh glacier, and at a subsequent one by the Irish Sea Glacier, and both of these streams entered the valley of the Trent or some of its affluents. From the eastward, again, the great North Sea Glacier encroached in like manner, carrying the Great Chalky Boulder-Clay even into the drainage area of the westward-flowing rivers near Coventry.

"The glacial geology of the Trent Valley from Burton to Nottingham has been ably dealt with by Mr. R. M. Deeley, who recognises a succession which may be generalised as follows: (1.) A lower series containing rocks derived from the Pennine chain; (2.) A middle series containing rocks from the eastward (chalky boulder-clay, etc.); and (3.) An upper series with Pennine rocks. Mr. Deeley thinks the Pennine débris may have been brought by glaciers flowing down the valleys of the Dove, the Wye, and the Derwent; but, while recognising the importance of the testimony adduced, especially that of the boulders, I am compelled to reserve judgment upon this point until something like moraines or other evidences of local glaciers can be shown in those valleys. In their upper parts there is not a sign of glaciation. Some of the deposits described must have been laid down by land-ice; while the conformation of the country shows that during some stages of glaciation a lake must have existed into which the different elements of the converging glaciers must have projected. This condition will account for the remarkable commingling of boulders observed in some of the deposits. Welsh, Cumbrian, and Scottish rocks occur in the western portion of the Trent Valley. The overflow of the extra-morainic lake would find its way into the valleys of the Avon and Severn, and may be taken to account for the abundance of flints in some of the gravels.

"The Isle of Man.--This little island in mid-seas constituted in the early stages of the Glacial epoch an independent centre of glaciation, and from some of its valleys ice-streams undoubtedly descended to the sea; but with the growth of the great Irish Sea Glacier the native ice was merged in the invading mass, and at the climax of the period the whole island was completely buried, even to its highest peak (Snae Fell, 2,054 feet), beneath the ice. The effects of this general glaciation are clearly seen in the mantle of unstratified drift material which overspread the hills; in the moutonnée appearance of the entire island; and in the transport of boulders of local rocks. The striations upon rock surfaces show a constancy of direction in agreement with the boulder-transport which can be ascribed to no other agency than a great continuous sheet of such dimensions as to ignore minor hills and valleys.

"The disposition of the striæ is equally conclusive, for we find that on a stepped escarpment of limestone both the horizontal and the vertical faces are striated continuously and obliquely from the one on to the other, showing that the ice had a power of accommodating itself to the surface over which it passed that could not be displayed by floating ice. There is a remarkable fact concerning the distribution of boulders on this island which would strike the most superficial observers, namely, that foreign rocks are confined to the low grounds. It might be argued that the local ice always retained its individuality, and so kept the foreign ice with its characteristic boulders at bay. But, apart from the a priori improbability of so small a hill-cluster achieving what the Lake District could not accomplish, the fact that Snae Fell, an isolated conical hill, is swathed in drift from top to bottom, is quite conclusive that the foreign ice must have got in. Why, then, did it carry no stones with it? The following suggestion I make not without misgivings, though there are many facts to which I might appeal that seem strongly corroborative:

"The hilly axis of the island runs in a general northeast and southwest direction, and it rises from a great expanse of drift in the north with singular abruptness, some of the hills being almost inaccessible to a direct approach without actual climbing. I imagine that the ice which bore down upon the northern end of the island was, so far as its lower strata were concerned, unable to ascend so steep an acclivity, and was cleft, and flowed to right and left. The upper ice, being of ice-sheet origin, would be relatively clean, and this flowing straight over the top of the obstruction would glaciate the country with such material as was lying loose upon the ground or could be dislodged by mere pressure. It would appear from published descriptions that the Isle of Arran offers the same problem, and I would suggest the application of the same solution to it.

"Marine shells occur in the Manx drift, but only in such situations as were reached by the ice-laden with foreign stones. They present similar features of association of shells of different habitat, and perhaps of geological age, to those already referred to as being common characteristics of the shell-faunas of the drift of the mainland. Four extinct species of mollusca have been recognised by me in the Manx drift.

"The Manx drift is of great interest as showing, perhaps better than any locality yet studied, those features of the distribution of boulders of native rocks which attest so clearly the exclusive action of land-ice. There are in the island many highly characteristic igneous rocks, and I have found that boulders of these rocks never occur to the northward of the parent mass, and very rarely in any direction except to the southwest.

"Cumming observed in regard to one rock, the Foxdale granite, that whereas the highest point at which it occurs in situ was 657 feet above sea-level, boulders of it occurred in profusion within 200 feet of the summit of South Barrule (1,585 feet), a hill two miles only, in a southwesterly direction, from the granite outcrop.

"They also occur on the summit of Cronk-na-Irrey-Lhaa, 1,449 feet above sea-level. The vertical uplift has been 728 and 792 feet respectively.

"In the low grounds of the north of the island a finely developed terminal moraine extends in a great sweep so as to obstruct the drainage and convert thousands of acres of land into lake and morass, which is only now yielding to artificial drainage. Many fine examples of drumlin and esker mounds occur at low levels in different parts of the island; and it was remarked nearly fifty years ago by Cumming, that their long axes were parallel to the direction of ice-movement indicated by the striated surfaces and the transport of boulders.

"The foreign boulders are mainly from the granite mountains of Galloway, but there are many flints, presumably from Antrim, a very small number of Lake District rocks, and a remarkable rock containing the excessively rare variety of hornblende, Riebeckite. This has now been identified with a rock on Ailsa Crag, a tiny islet in the Frith of Clyde; and a Manx geologist, the Rev. S. N. Harrison, has discovered a single boulder of the highly characteristic pitchstone of Corriegills, in the Isle of Arran.

"The So-called Great Submergence.

"It may be convenient to adduce some additional facts which render the theory of a great submergence of the country south of the Cheviots untenable.

"The sole evidence upon which it rests is the occurrence of shells, mostly in an extremely fragmentary condition, in deposits occurring at various levels up to about 1,400 feet above sea-level: A little space may profitably be devoted to a criticism of this evidence.

"Moel Tryfaen ('The Hill of the Three Rocks').--This celebrated locality is on the first rise of the ground between the Menai Straits and the congeries of hills constituting 'Snowdonia'; and when we look to the northward from the top of the hill (1,350 feet) we see the ground rising from the straits in a series of gentle undulations whose smooth contours would be found from a walk across the country to be due to the thick mask of glacial deposits which obliterates the harsher features of the solid rocks.

"The deposits on Moel Tryfaen are exposed in a slate-quarry on the northern aspect of the hill near the summit, and consist of two wedges of structureless boulder-clay, each thinning towards the top of the hill. The lower mass of clay, wherever it rests upon the rock, contains streaks and irregular patches of eccentric form, of sharp, perfectly angular fragments of slate; and the underlying rock may be seen to be crushed and broken, its cleavage-laminæ being thrust over from northwest to southeast--that is, up-hill. The famous 'shell-bed' is a thick series of sands and gravels interosculated with the clays on the slope of the hill, but occupying the entire section above the slate towards the top. The bedding shows unmistakable signs of the action of water, both regular stratification and false bedding being well displayed. The stones occurring in the clays are mainly if not entirely Welsh, including some from the interior of the country, and they are not infrequently of large size--two or three tons' weight--and well scratched.

"The stones found in the sands and gravels include a great majority of local rocks, but besides these there have been recorded the following:

Rock. Source. Highest Minimum point uplift in situ. in feet.

Granite Eskdale, Cumberland 1,286 64 Granite Criffel, Galloway ..... ... Flint Antrim (?) 1,000 350 To these I can add: Granophyre Buttermere, Cumberland ..... ... Eurite Ailsa Craig, Frith of Clyde 1,097 253

"The shells in the Moel Tryfaen deposit have been fully described, so far as the enumeration of species and relative frequency are concerned, but little has been said as to their absolute abundance and their condition. The shells are extremely rare, and daring a recent visit a party of five persons, in an assiduous search of about two hours, succeeded in finding five whole shells and about two ounces of fragments. The opportunities for collecting are as good as could be desired. The sections exposed have an aggregate length of about a quarter of a mile, with a height varying from ten to twenty feet of the shelly portion; and besides this there are immense spoil-banks, upon whose rain-washed slopes fossil-collecting can be carried on under the most favorable conditions.

"I would here remark, that the occurrence of small seams of shelly material of exceptional richness has impressed collectors with the idea that they were dealing with a veritable shell-bed, when the facts would bear a very different interpretation. A fictitious abundance is brought about by a process of what may be termed 'concentration,' by the action of a gently flowing current of water upon materials of different sizes and different specific gravities. Shells when but recently vacated consist of materials of rather high specific gravity, penetrated by pores containing animal matter, so that the density of the whole mass is far below that of rocks in general, and hence a current too feeble to move pebbles would yet carry shells. Illustrations of this process may be observed upon any shore in the concentration of fragments of coal, corks, or other light material.

"Regarding the interpretation of these facts: The commonly received idea is, that the beds were laid down in the sea during a period of submergence, and that the shells lived, not perhaps on the spot, but somewhere near, and that the terminal curvature of the slate was produced by the grounding of icebergs which also brought the boulders. But if this hypothesis were accepted, it would be necessary to invest the flotation of ice with a constancy of direction entirely at variance with observed facts, for the phenomena of terminal curvature is shown" with perfect persistence of direction wherever the boulder-clay rests upon the rock; and, further, there is the highly significant fact, that neither the sands and gravels nor the rock upon which they rest show any signs of disturbance or contortion, such as must have been produced if floating ice had been an operative agent.

"The uplift of foreign rocks is equally significant; and when we take into account the great distances from which they have been borne and the frequency with which such an operation must have been repeated, the inadequacy becomes apparent of Darwin's ingenious suggestion, that it might have been effected by a succession of uplifts by shore-ice during a period of slow subsidence; while the character and abundance of the molluscan remains invest with a species of irony the application of the term 'shell-bed' to the deposit.

"I now turn to the alternative explanation (see ante, p. 145), viz., that the whole of the phenomena were produced by a mass of land-ice which was forced in upon Moel Tryfaen from the north or northwest, overpowering any Welsh ice which obstructed its course. This view is in harmony with the observations regarding the 'terminal curvature' of the slates, the occurrence of sharp angular chips of slate in the boulder-clay, and the coincidence of direction of these indications of movement with the carry of foreign stones. The few shells and shell-crumbs in the sands and gravels would, upon this hypothesis, be the infinitesimal relics of huge shell-banks in the Irish Sea which were destroyed by the glacier and in part incorporated in its ground-moraine or involved in the ice itself. The sands and gravels would represent the wash which would take place wherever, by the occurrence of a 'nunatak' or by approach to the edge of the ice, water could have a free escape.

"Two principal objections have been urged to the land-ice explanation of the Moel Tryfaen deposits. An able critic asks, 'Can, then, ice walk up-hill?' To this we answer, Given a sufficient 'head' behind it, and ice can certainly achieve that feat, as every roche moutonnée proves. If it be granted that ice on the small scale can move up-hill, there is no logical halting-place between the uplift of ten or twenty feet to surmount a roche moutonnée, and an equally gradual elevation to the height of Moel Tryfaen. Furthermore, the inland ice of Greenland is known to extrude its ground-moraine on the 'weather-side' of the nunataks, and the same action would account for the material uplifted on Moel Tryfaen.

"The second objection brought forward was couched in somewhat these terms: 'If the Lake District had its ice-sheet, surely Wales had one also. Could not Snowdonia protect the heart of its own domain?' Of course, Wales had its ice-sheet, and the question so pointedly raised by the objector needs an answer; and though it is merely a question of how much force is requisite to overcome a certain resistance (both factors being unknown), still there are features in the case which render it specially interesting and at the same time comparatively easy of explanation. It seems rather like stating a paradox, yet the fact is, that it was the proximity of Snowdon which, in my opinion, enabled the foreign ice to invade Wales at that point.

"A glance at the map will show that the 'radiant point' of the Welsh ice was situated on or near Arenig Mawr, and that the great mass of Snowdon stands quite on the periphery of the mountainous regions of North Wales, so that it would oppose its bulk to fend off the native ice-sheet and prevent it from extending seaward in that direction.

"As a consequence, the only Welsh ice in position to obstruct the onward march of the invader would be such trifling valley-glaciers as could form on the western slopes of Snowdon itself.

"The peak of Snowdon is 3,570 feet above sea-level, and Arenig Mawr, 2,817 feet high, is eighteen miles to the eastward, and a broad, deep valley with unobstructed access to Cardigan Bay intervenes; so, if any ice from the central mass made its way over the Snowdonian range, it performed a much more surprising feat than that involved in the ascent of Moel Tryfaen from the westward.

"The profile shows in diagrammatic form the probable relations of the foreign to the native ice at the time when the Moel Tryfaen deposits were laid down.

"From what has been said regarding the great glaciers, it would seem that ice advanced upon the land from the seaward in several parts of the coast of England, Wales, and the Isle of Man. Now, it is in precisely those parts of the country, and those alone, that the remains of marine animals occur in the glacial deposits. If the dispersal of the shells found in the drift had been effected by the means I have suggested, it would follow, as an inevitable consequence, that wherever shells occur there should also be boulders which have been brought from beyond the sea. This I find to be the case, and in two instances the discovery of shells was preliminary to the extension of the boundaries of the known distribution of boulders of trans-marine origin.

"The officers of the Geological Survey some years ago observed the occurrence of 'obscure fragments of marine shells' in a deposit at Whalley, Lancashire, in which they could find only local rocks. One case such as this would be fatal to the theory of the remanié origin of the shells, but on visiting the section with Mr. W. A. Downham, I found, amongst the very few stones which occurred in the shell-bearing sand at the spot indicated, two well-marked examples of Cumbrian volcanic rocks, and, at a little distance, large boulders of Scottish granites.

"The second case is more striking. The announcement was made that shells had been found on a hill called Gloppa near Oswestry, in Shropshire, and, as it lay about five miles to the westward of Mackintosh's boundary of the Irish Sea Glacier, and therefore well within the area of exclusively Welsh boulders, it furnished an excellent opportunity of putting the theory to the test. An examination of the boulders associated with the shells showed that the whole suite of Galloway and Cumbrian erratics such as belong to the Irish Sea Glacier were present in great abundance. Not only this, but in the midst of the series of shell-bearing gravels I observed a thin lenticular bed of greenish clay, which upon examination was found to be crowded with well-scratched specimens of Welsh rocks; but neither a morsel of shell nor a single pebble of a foreign rock could be found, either by a careful examination in the field or by washing the clay at home, and examining with a lens the sand and stones separated out.

"The fact that predictions such as these have been verified affords a very striking corroboration of the theory put forward; and, though shells cannot be found in every deposit in which they might, ex hypothesi, be found, yet the strict limitation of them to situations which conform to those assigned upon theoretical grounds cannot be ascribed to mere coincidence. If the land had ever been submerged during any part of the Glacial epoch to a depth of 1,400 feet, it is inconceivable that clear and indisputable evidence should not be found in abundance in the sheltered valleys of the Lake District and Wales, which would have been deep, quiet fiords, in which vast colonies of marine creatures would have found harbour, as they do in the deep lochs of Scotland to-day.

"It has been urged, in explanation of this absence of marine remains in the great hill-centres, that the 'second glaciation' might have destroyed them; but to do this would require that the ice should make a clean and complete sweep of all the loose deposits both in the hollows of the valleys and on the hill-sides, and further that it should destroy all the shells and all the foreign stones which floated in during the submergence. At the same time we should have to suppose that the drift which lay in the paths of the great glaciers was not subjected to any interference whatever. But, assuming that these difficulties were explained, there would still remain the fact that the valleys which have never been glaciated--as, for example, those of Derbyshire--show no signs whatever of any marine deposits, nor of marine action in any form whatever.

"The sea leaves other traces also, besides shells, of its presence in districts that have really been submerged, yet there are no signs whatever to be found of them in all England, except the post-glacial raised beaches. Furthermore, in all the area occupied by glacial deposits there are no true sea-beaches, no cliffs nor sea-worn caves, no barnacle-encrusted rocks, nor rocks bored by Pholas or Saxicava. Are we to believe that these never existed; or that, having existed, they have been obliterated by subsequent denudations? To make good the former proposition, it would be necessary as a preliminary to show that the movement of subsidence and re-elevation was so rapid, and the interval between so brief, that no time was allowed for any marine erosion to take place. If this were so, it would be the most stupendous catastrophe of which we have any geological record; but we are not left in doubt regarding the duration of the submerged condition, for the occurrence of forty feet of gravel upon the summits of the hills indicates plainly that, if they were accumulated by the sea, the land must have stood at that level for a very long period, amply sufficient for the formation of a well-marked coast-line.

"The alternative proposition, that post-glacial denudation had removed the traces of subsidence, is equally at variance with the evidence. Post-glacial denudation has left kames and drumlins, and all the other forms of glacial deposits, in almost perfect integrity; the small kettle-holes are not yet filled up; and it is therefore quite out of the question that the far more enduring features, such as sea-cliffs, shore platforms, and beaches, should have been destroyed.

"The only reasonable conclusion is, that these evidences of marine action never existed, because the land in glacial times was never depressed below its present level. If the level were different at all (as I think may have been the case on the western side of England), it was higher, and not lower.

"The details of the submergence hypothesis have, so far as I am aware, never been dealt with by its advocates, otherwise I cannot but think that it would have been abandoned long since. It has been stated in general terms that the subsidence was greatest in the north and diminished to zero in the south, but no attempt was made to trace the evidence of extreme subsidence across country and along the principal hill-ranges--in fact, to see how it varied in every direction.

"If we take a traverse of England, say from Flamborough Head upon the east to Moel Tryfaen on the west, and accept as evidence of submergence any true glacial deposits (except, as in the case of the interior of Wales, the deposits are obviously the effects of purely local glaciers and contain, therefore, no shells), we shall find that the subsidence, if any, must have been not simply differential but sporadic.