Volume 1 Part 1 Page 28 There Is an Account by Mr. Ducatel of Vast Beds

of oysters and clams having been destroyed by the gradual filling up of the shallow lagoons and channels, on the shores of the southern United States. At Chiloe, in South America, I heard of a similar loss, sustained by the inhabitants, in the disappearance from one part of the coast of an edible species of Ascidia.)

Evidence more or less distinct of a change of level between the land and water, has been detected on almost all the land on this side of the globe. Captain Grey, and other travellers, have found in Southern Australia upraised shells, belonging either to the recent, or to a late tertiary period. The French naturalists in Baudin’s expedition, found shells similarly circumstanced on the S.W. coast of Australia. The Rev. W.B. Clarke finds proofs of the elevation of the land, to the amount of 400 feet, at the Cape of Good Hope. (“Proceedings of the Geological Society” volume 3 page 420.) In the neighbourhood of the Bay of Islands in New Zealand, I observed that the shores were scattered to some height, as at Van Diemen’s Land, with sea-shells, which the colonists attribute to the natives. (I will here give a catalogue of the rocks which I met with near the Bay of Islands, in New Zealand:—1st, Much basaltic lava, and scoriform rocks, forming distinct craters;—2nd, A castellated hill of horizontal strata of flesh-coloured limestone, showing when fractured distinct crystalline facets: the rain has acted on this rock in a remarkable manner, corroding its surface into a miniature model of an Alpine country: I observed here layers of chert and clay ironstone; and in the bed of a stream, pebbles of clay-slate;—3rd, The shores of the Bay of Islands are formed of a feldspathic rock, of a bluish-grey colour, often much decomposed, with an angular fracture, and crossed by numerous ferruginous seams, but without any distinct stratification or cleavage. Some varieties are highly crystalline, and would at once be pronounced to be trap; others strikingly resembled clay-slate, slightly altered by heat: I was unable to form any decided opinion on this formation.) Whatever may have been the origin of these shells, I cannot doubt, after having seen a section of the valley of the Thames River (37 degrees S.), drawn by the Rev. W. Williams, that the land has been there elevated: on the opposite sides of this great valley, three step-like terraces, composed of an enormous accumulation of rounded pebbles, exactly correspond with each other: the escarpment of each terrace is about fifty feet in height. No one after having examined the terraces in the valleys on the western shores of South America, which are strewed with sea-shells, and have been formed during intervals of rest in the slow elevation of the land, could doubt that the New Zealand terraces have been similarly formed. I may add, that Dr. Dieffenbach, in his description of the Chatham Islands (“Geographical Journal” volume 11 pages 202, 205.) (S.W. of New Zealand), states that it is manifest “that the sea has left many places bare which were once covered by its waters.”

KING GEORGE’S SOUND.

This settlement is situated at the south-western angle of the Australian continent: the whole country is granitic, with the constituent minerals sometimes obscurely arranged in straight or curved laminae. In these cases, the rock would be called by Humboldt, gneiss-granite, and it is remarkable that the form of the bare conical hills, appearing to be composed of great folding layers, strikingly resembles, on a small scale, those composed of gneiss-granite at Rio de Janeiro, and those described by Humboldt at Venezuela. These plutonic rocks are, in many places, intersected by trappean-dikes; in one place, I found ten parallel dikes ranging in an E. and W. line; and not far off another set of eight dikes, composed of a different variety of trap, ranging at right angles to the former ones. I have observed in several primary districts, the occurrence of systems of dikes parallel and close to each other.

SUPERFICIAL FERRUGINOUS BEDS.

The lower parts of the country are everywhere covered by a bed, following the inequalities of the surface, of a honeycombed sandstone, abounding with oxides of iron. Beds of nearly similar composition are common, I believe, along the whole western coast of Australia, and on many of the East Indian islands. At the Cape of Good Hope, at the base of the mountains formed of granite and capped with sandstone, the ground is everywhere coated either by a fine-grained, rubbly, ochraceous mass, like that at King George’s Sound, or by a coarser sandstone with fragments of quartz, and rendered hard and heavy by an abundance of the hydrate of iron, which presents, when freshly broken, a metallic lustre. Both these varieties have a very irregular texture, including spaces either rounded or angular, full of loose sand: from this cause the surface is always honeycombed. The oxide of iron is most abundant on the edges of the cavities, where alone it affords a metallic fracture. In these formations, as well as in many true sedimentary deposits, it is evident that iron tends to become aggregated, either in the form of a shell, or of a network. The origin of these superficial beds, though sufficiently obscure, seems to be due to alluvial action on detritus abounding with iron.

SUPERFICIAL CALCAREOUS DEPOSIT.

A calcareous deposit on the summit of Bald Head, containing branched bodies, supposed by some authors to have been corals, has been celebrated by the descriptions of many distinguished voyagers. (I visited this hill, in company with Captain Fitzroy, and we came to a similar conclusion regarding these branching bodies.) It folds round and conceals irregular hummocks of granite, at the height of 600 feet above the level of the sea. It varies much in thickness; where stratified, the beds are often inclined at high angles, even as much as at thirty degrees, and they dip in all directions. These beds are sometimes crossed by oblique and even-sided laminae. The deposit consists either of a fine, white calcareous powder, in which not a trace of structure can be discovered, or of exceedingly minute, rounded grains, of brown, yellowish, and purplish colours; both varieties being generally, but not always, mixed with small particles of quartz, and being cemented into a more or less perfect stone. The rounded calcareous grains, when heated in a slight degree, instantly lose their colours; in this and in every other respect, closely resembling those minute, equal- sized particles of shells and corals, which at St. Helena have been drifted up the side of the mountains, and have thus been winnowed of all coarser fragments. I cannot doubt that the coloured calcareous particles here have had a similar origin. The impalpable powder has probably been derived from the decay of the rounded particles; this certainly is possible, for on the coast of Peru, I have traced LARGE UNBROKEN shells gradually falling into a substance as fine as powdered chalk. Both of the above-mentioned varieties of calcareous sandstone frequently alternate with, and blend into, thin layers of a hard substalagmitic rock, which, even when the stone on each side contains particles of quartz, is entirely free from them (I adopt this term from Lieutenant Nelson’s excellent paper on the Bermuda Islands “Geolog. Trans.” volume 5 page 106, for the hard, compact, cream- or brown- coloured stone, without any crystalline structure, which so often accompanies superficial calcareous accumulations. I have observed such superficial beds, coated with substalagmitic rock, at the Cape of Good Hope, in several parts of Chile, and over wide spaces in La Plata and Patagonia. Some of these beds have been formed from decayed shells, but the origin of the greater number is sufficiently obscure. The causes which determine water to dissolve lime, and then soon to redeposit it, are not, I think, known. The surface of the substalagmitic layers appears always to be corroded by the rain-water. As all the above-mentioned countries have a long dry season, compared with the rainy one, I should have thought that the presence of the substalagmitic was connected with the climate, had not Lieutenant Nelson found this substance forming under sea-water. Disintegrated shell seems to be extremely soluble; of which I found good evidence, in a curious rock at Coquimbo in Chile, which consisted of small, pellucid, empty husks, cemented together. A series of specimens clearly showed that these husks had originally contained small rounded particles of shells, which had been enveloped and cemented together by calcareous matter (as often happens on sea-beaches), and which subsequently had decayed, and been dissolved by water, that must have penetrated through the calcareous husks, without corroding them,—of which processes every stage could be seen.): hence we must suppose that these layers, as well as certain vein- like masses, have been formed by rain dissolving the calcareous matter and re-precipitating it, as has happened at St. Helena. Each layer probably marks a fresh surface, when the, now firmly cemented, particles existed as loose sand. These layers are sometimes brecciated and re-cemented, as if they had been broken by the slipping of the sand when soft. I did not find a single fragment of a sea-shell; but bleached shells of the Helix melo, an existing land species, abound in all the strata; and I likewise found another Helix, and the case of an Oniscus.

The branches are absolutely undistinguishable in shape from the broken and upright stumps of a thicket; their roots are often uncovered, and are seen to diverge on all sides; here and there a branch lies prostrate. The branches generally consist of the sandstone, rather firmer than the surrounding matter, with the central parts filled, either with friable, calcareous matter, or with a substalagmitic variety; this central part is also frequently penetrated by linear crevices, sometimes, though rarely, containing a trace of woody matter. These calcareous, branching bodies, appear to have been formed by fine calcareous matter being washed into the casts or cavities, left by the decay of branches and roots of thickets, buried under drifted sand. The whole surface of the hill is now undergoing disintegration, and hence the casts, which are compact and hard, are left projecting. In calcareous sand at the Cape of Good Hope, I found the casts, described by Abel, quite similar to these at Bald Head; but their centres are often filled with black carbonaceous matter not yet removed. It is not surprising, that the woody matter should have been almost entirely removed from the casts on Bald Head; for it is certain, that many centuries must have elapsed since the thickets were buried; at present, owing to the form and height of the narrow promontory, no sand is drifted up, and the whole surface, as I have remarked, is wearing away. We must, therefore, look back to a period when the land stood lower, of which the French naturalists (See M. Peron “Voyage” tome 1 page 204.) found evidence in upraised shells of recent species, for the drifting on Bald Head of the calcareous and quartzose sand, and the consequent embedment of the vegetable remains. There was only one appearance which at first made me doubt concerning the origin of the cast,—namely, that the finer roots from different stems sometimes became united together into upright plates or veins; but when the manner is borne in mind in which fine roots often fill up cracks in hard earth, and that these roots would decay and leave hollows, as well as the stems, there is no real difficulty in this case. Besides the calcareous branches from the Cape of Good Hope, I have seen casts, of exactly the same forms, from Madeira* and from Bermuda; at this latter place, the surrounding calcareous rocks, judging from the specimens collected by Lieutenant Nelson, are likewise similar, as is their subaerial formation. Reflecting on the stratification of the deposit on Bald Head,—on the irregularly alternating layers of substalagmitic rock,—on the uniformly sized, and rounded particles, apparently of sea-shells and corals,—on the abundance of land-shells throughout the mass,—and finally, on the absolute resemblance of the calcareous casts, to the stumps, roots, and branches of that kind of vegetation, which would grow on sand-hillocks, I think there can be no reasonable doubt, notwithstanding the different opinion of some authors, that a true view of their origin has been here given.

*(Dr. J. Macaulay has fully described (“Edinb. New Phil. Journ.” volume 29 page 350) the casts from Madeira. He considers (differently from Mr. Smith of Jordan Hill) these bodies to be corals, and the calcareous deposit to be of subaqueous origin. His arguments chiefly rest (for his remarks on their structure are vague) on the great quantity of the calcareous matter, and on the casts containing animal matter, as shown by their evolving ammonia. Had Dr. Macaulay seen the enormous masses of rolled particles of shells and corals on the beach of Ascension, and especially on coral-reefs; and had he reflected on the effects of long-continued, gentle winds, in drifting up the finer particles, he would hardly have advanced the argument of quantity, which is seldom trustworthy in geology. If the calcareous matter has originated from disintegrated shells and corals, the presence of animal matter is what might have been expected. Mr. Anderson analysed for Dr. Macaulay part of a cast, and he found it composed of:—

Carbonate of lime......73.15 Silica.................11.90 Phosphate of lime.......8.81 Animal matter...........4.25 Sulphate of lime......a trace 98.11)

Calcareous deposits, like these of King George’s Sound, are of vast extent on the Australian shores. Dr. Fitton remarks, that “recent calcareous breccia (by which term all these deposits are included) was found during Baudin’s voyage, over a space of no less than twenty-five degrees of latitude and an equal extent of longitude, on the southern, western, and north-western coasts.” (For ample details on this formation consult Dr. Fitton “Appendix to Captain King’s Voyage.” Dr. Fitton is inclined to attribute a concretionary origin to the branching bodies: I may remark, that I have seen in beds of sand in La Plata cylindrical stems which no doubt thus originated; but they differed much in appearance from these at Bald Head, and the other places above specified.) It appears also from M. Peron, with whose observations and opinions on the origin of the calcareous matter and branching casts mine entirely accord, that the deposit is generally much more continuous than near King George’s Sound. At Swan River, Archdeacon Scott states that in one part it extends ten miles inland. (“Proceedings of the Geolog. Soc.” volume 1 page 320.) Captain Wickham, moreover, informs me that during his late survey of the western coast, the bottom of the sea, wherever the vessel anchored, was ascertained, by crowbars being let down, to consist of white calcareous matter. Hence it seems that along this coast, as at Bermuda and at Keeling Atoll, submarine and subaerial deposits are contemporaneously in process of formation, from the disintegration of marine organic bodies. The extent of these deposits, considering their origin, is very striking; and they can be compared in this respect only with the great coral-reefs of the Indian and Pacific Oceans. In other parts of the world, for instance in South America, there are SUPERFICIAL calcareous deposits of great extent, in which not a trace of organic structure is discoverable; these observations would lead to the inquiry, whether such deposits may not, also, have been formed from disintegrated shells and corals.

CAPE OF GOOD HOPE.

After the accounts given by Barrow, Carmichael, Basil Hall, and W.B. Clarke of the geology of this district, I shall confine myself to a few observations on the junction of the three principal formations. The fundamental rock is granite (In several places I observed in the granite, small dark-coloured balls, composed of minute scales of black mica in a tough basis. In another place, I found crystals of black schorl radiating from a common centre. Dr. Andrew Smith found, in the interior parts of the country, some beautiful specimens of granite, with silvery mica radiating or rather branching, like moss, from central points. At the Geological Society, there are specimens of granite with crystallised feldspar branching and radiating in like manner.), overlaid by clay-slate: the latter is generally hard, and glossy from containing minute scales of mica; it alternates with, and passes into, beds of slightly crystalline, feldspathic, slaty rock. This clay-slate is remarkable from being in some places (as on the Lion’s Rump) decomposed, even to the depth of twenty feet, into a pale-coloured, sandstone-like rock, which has been mistaken, I believe, by some observers, for a separate formation. I was guided by Dr. Andrew Smith to a fine junction at Green Point between the granite and clay-slate: the latter at the distance of a quarter of a mile from the spot, where the granite appears on the beach (though, probably, the granite is much nearer underground), becomes slightly more compact and crystalline. At a less distance, some of the beds of clay-slate are of a homogeneous texture, and obscurely striped with different zones of colour, whilst others are obscurely spotted. Within a hundred yards of the first vein of granite, the clay-slate consists of several varieties; some compact with a tinge of purple, others glistening with numerous minute scales of mica and imperfectly crystallised feldspar; some obscurely granular, others porphyritic with small, elongated spots of a soft white mineral, which being easily corroded, gives to this variety a vesicular appearance. Close to the granite, the clay-slate is changed into a dark-coloured, laminated rock, having a granular fracture, which is due to imperfect crystals of feldspar, coated by minute, brilliant scales of mica.

The actual junction between the granitic and clay-slate districts extends over a width of about two hundred yards, and consists of irregular masses and of numerous dikes of granite, entangled and surrounded by the clay- slate: most of the dikes range in a N.W. and S.E. line, parallel to the cleavage of the slate. As we leave the junction, thin beds, and lastly, mere films of the altered clay-slate are seen, quite isolated, as if floating, in the coarsely crystallised granite; but although completely detached, they all retain traces of the uniform N.W. and S.E. cleavage. This fact has been observed in other similar cases, and has been advanced by some eminent geologists (See M. Keilhau “Theory on Granite” translated in the “Edinburgh New Philosophical Journal” volume 24 page 402.), as a great difficulty on the ordinary theory, of granite having been injected whilst liquified; but if we reflect on the probable state of the lower surface of a laminated mass, like clay-slate, after having been violently arched by a body of molten granite, we may conclude that it would be full of fissures parallel to the planes of cleavage; and that these would be filled with granite, so that wherever the fissures were close to each other, mere parting layers or wedges of the slate would depend into the granite. Should, therefore, the whole body of rock afterwards become worn down and denuded, the lower ends of these dependent masses or wedges of slate would be left quite isolated in the granite; yet they would retain their proper lines of cleavage, from having been united, whilst the granite was fluid, with a continuous covering of clay-slate.

Following, in company with Dr. A. Smith, the line of junction between the granite and the slate, as it stretched inland, in a S.E. direction, we came to a place, where the slate was converted into a fine-grained, perfectly characterised gneiss, composed of yellow-brown granular feldspar, of abundant black brilliant mica, and of few and thin laminae of quartz. From the abundance of the mica in this gneiss, compared with the small quantity and excessively minute scales, in which it exists in the glossy clay-slate, we must conclude, that it has been here formed by the metamorphic action—a circumstance doubted, under nearly similar circumstances, by some authors. The laminae of the clay-slate are straight; and it was interesting to observe, that as they assumed the character of gneiss, they became undulatory with some of the smaller flexures angular, like the laminae of many true metamorphic schists.

SANDSTONE FORMATION.

This formation makes the most imposing feature in the geology of Southern Africa. The strata are in many parts horizontal, and attain a thickness of about two thousand feet. The sandstone varies in character; it contains little earthy matter, but is often stained with iron; some of the beds are very fine-grained and quite white; others are as compact and homogeneous as quartz rock. In some places I observed a breccia of quartz, with the fragments almost dissolved in a siliceous paste. Broad veins of quartz, often including large and perfect crystals, are very numerous; and it is evident in nearly all the strata, that silica has been deposited from solution in remarkable quantity. Many of the varieties of quartzite appeared quite like metamorphic rocks; but from the upper strata being as siliceous as the lower, and from the undisturbed junctions with the granite, which in many places can be examined, I can hardly believe that these sandstone-strata have been exposed to heat. (The Rev. W.B. Clarke, however, states, to my surprise (“Geolog. Proceedings” volume 3 page 422), that the sandstone in some parts is penetrated by granitic dikes: such dikes must belong to an epoch altogether subsequent to that when the molten granite acted on the clay-slate.) On the lines of junction between these two great formations, I found in several places the granite decayed to the depth of a few inches, and succeeded, either by a thin layer of ferruginous shale, or by four or five inches in thickness of the re-cemented crystals of the granite, on which the great pile of sandstone immediately rested.

Mr. Schomburgk has described (“Geographical Journal” volume 10 page 246.) a great sandstone formation in Northern Brazil, resting on granite, and resembling to a remarkable degree, in composition and in the external form of the land, this formation of the Cape of Good Hope. The sandstones of the great platforms of Eastern Australia, which also rest on granite, differ in containing more earthy and less siliceous matter. No fossil remains have been discovered in these three vast deposits. Finally, I may add that I did not see any boulders of far-transported rocks at the Cape of Good Hope, or on the eastern and western shores of Australia, or at Van Diemen’s Land. In the northern island of New Zealand, I noticed some large blocks of greenstone, but whether their parent rock was far distant, I had no opportunity of determining.

INDEX TO VOLCANIC ISLANDS.

Abel, M., on calcareous casts at the Cape of Good Hope.

Abingdon island.

Abrolhos islands, incrustation on.

Aeriform explosions at Ascension.

Albatross, driven from St. Helena.

Albemarle island.

Albite, at the Galapagos archipelago.

Amygdaloidal cells, half filled.

Amygdaloids, calcareous origin of.

Ascension, arborescent incrustation on rocks of. -absence of dikes, freedom from volcanic action, and state of lava-streams.

Ascidia, extinction of.

Atlantic Ocean, new volcanic focus in.

Augite, fused.

Australia.

Azores.

Bahia in Brazil, dikes at.

Bailly, M., on the mountains of Mauritius.

Bald Head.

Banks’ Cove.

Barn, The, St. Helena.

Basalt, specific gravity of.

Basaltic coast-mountains at Mauritius. -at St. Helena. -at St. Jago.

Beaumont, M. Elie de, on circular subsidences in lava. -on dikes indicating elevation. -on inclination of lava-streams. -on laminated dikes.

Bermuda, calcareous rocks of.

Beudant, M., on bombs. -on jasper. -on laminated trachyte. -on obsidian of Hungary. -on silex in trachyte.

Bole.

Bombs, volcanic.

Bory St. Vincent, on bombs.

Boulders, absence in Australia and Cape of Good Hope.

Brattle island.

Brewster, Sir D., on a calcareo-animal substance. -on decomposed glass.

Brown, Mr. R., on extinct plants from Van Diemen’s land. -on sphaerulitic bodies in silicified wood.

Buch, Von, on cavernous lava. -on central volcanoes. -on crystals sinking in obsidian. -on laminated lava. -on obsidian streams. -on olivine in basalt. -on superficial calcareous beds in the Canary islands.

Calcareous deposit at St. Jago affected by heat. -fibrous matter, entangled in streaks in scoriae. -freestone at Ascension. -incrustations at Ascension. -sandstone at St. Helena. -superficial beds at King George’s sound.

Cape of Good Hope.

Carbonic acid, expulsion of, by heat.

Carmichael, Capt., on glassy coatings to dikes.

Casts, calcareous, of branches.

Chalcedonic nodules.

Chalcedony in basalt and in silicified wood.

Chatham island.

Chlorophaeite.

Clarke, Rev. W., on the Cape of Good Hope.

Clay-slate, its decomposition and junction with granite at the Cape of Good Hope.

Cleavage of clay-slate in Australia.

Cleavage, cross, in sandstone.

Coast denudation at St. Helena.

Columnar basalt.

“Comptes Rendus,” account of volcanic phenomena in the Atlantic.

Concepcion, earthquake of.

Concretions in aqueous and igneous rocks compared. -in tuff. -of obsidian.

Conglomerate, recent, at St. Jago.

Coquimbo, curious rock of.

Corals, fossil, from Van Diemen’s Land.

Crater, segment of, at the Galapagos. -great central one at St. Helena. -internal ledges round, and parapet on.

Craters, basaltic, at Ascension. -form of, affected by the trade wind. -of elevation. -of tuff at Terceira. -of tuff at the Galapagos archipelago. -their breached state. -small basaltic at St. Jago. —at the Galapagos archipelago.

Crystallisation favoured by space.

Dartigues, M., on sphaerulites.

Daubeny, Dr., on a basin-formed island. -on fragments in trachyte.

D’Aubuisson on hills of phonolite. -on the composition of obsidian. -on the lamination of clay-slate.

De la Beche, Sir H., on magnesia in erupted lime. -on specific gravity of limestones.

Denudation of coast at St. Helena.

Diana’s Peak, St. Helena.

Dieffenbach, Dr., on the Chatham Islands.

Dikes, truncated, on central crateriform ridge of St. Helena. -at St. Helena; number of; coated by a glossy layer; uniform thickness of. -great parallel ones at St. Helena. -not observed at Ascension. -of tuff. -of trap in the plutonic series. -remnants of, extending far into the sea round St. Helena.

Dislocations at Ascension. -at St. Helena.

Distribution of volcanic islands.

Dolomieu, on decomposed trachyte. -on laminated lava. -on obsidian.

Dree, M., on crystals sinking in lava.

Dufrenoy, M., on the composition of the surface of certain lava-streams. -on the inclination of tuff-strata.

Eggs of birds embedded at St. Helena. -of turtle at Ascension.

Ejected fragments at Ascension. -at the Galapagos archipelago.

Elevation of St. Helena. -the Galapagos archipelago. -Van Diemen’s Land, Cape of Good Hope, New Zealand, Australia, and Chatham island. -of volcanic islands.

Ellis, Rev. W., on ledges within the great crater at Hawaii. -on marine remains at Otaheite.

Eruption, fissures of.

Extinction of land-shells at St. Helena.

Faraday, Mr., on the expulsion of carbonic acid gas.

Feldspar, fusibility of. -in radiating crystals. -Labrador, ejected.

Feldspathic lavas. -at St. Helena. -rock, alternating with obsidian. -lamination, and origin of.

Fernando Noronha.

Ferruginous superficial beds.

Fibrous calcareous matter at St. Jago.

Fissures of eruption.

Fitton, Dr., on calcareous breccia.

Flagstaff Hill, St. Helena.

Fleurian de Bellevue on sphaerulites.

Fluidity of lavas.

Forbes, Professor, on the structure of glaciers.

Fragments ejected at Ascension. -at the Galapagos archipelago.

Freshwater Bay.

Fuerteventura (Feurteventura), calcareous beds of.

Galapagos archipelago. -parapets round craters.

Gay Lussac, on the expulsion of carbonic acid gas.

Glaciers, their structure.

Glossiness of texture, origin of.

Gneiss, derived from clay-slate. -with a great embedded fragment.

Gneiss-granite, form of hills of.

Good Hope, Cape of.

Gorges, narrow, at St. Helena.

Granite, junction with clay-slate, at the Cape of Good Hope.

Granitic ejected fragments.

Gravity, specific, of lavas.

Gypsum, at Ascension. -in volcanic strata at St. Helena. -on surface of the ground at ditto.

Hall, Sir J., on the expulsion of carbonic acid gas.

Heat, action of, on calcareous matter.

Hennah, Mr., on ashes at Ascension.

Henslow, Prof., on chalcedony.

Hoffmann, on decomposed trachyte.

Holland, Dr., on Iceland.

Horner, Mr., on a calcareo-animal substance. -on fusibility of feldspar.

Hubbard, Dr., on dikes.

Humboldt on ejected fragments. -on obsidian formations. -on parapets round craters. -on sphaerulites.

Hutton on amygdaloids.

Hyalite in decomposed trachyte.

Iceland, stratification of the circumferential hills.

Islands, volcanic, distribution of. -their elevation.

Incrustation, on St. Paul’s rocks.

Incrustations, calcareous, at Ascension.

Jago, St.

James island.

Jasper, origin of.

Jonnes, M. Moreau de, on craters affected by wind.

Juan Fernandez.

Keilhau, M., on granite.

Kicker Rock.

King George’s sound.

Labrador feldspar, ejected.

Lakes at bases of volcanoes.

Lamination of volcanic rocks.

Land-shells, extinct, at St. Helena.

Lanzarote, calcareous beds of.

Lava, adhesion to sides of a gorge. -feldspathic. -with cells semi-amygdaloidal.

Lavas, specific gravity of.

Lava-streams blending together at St. Jago. -composition of surface of. -differences in the state of their surfaces. -extreme thinness of. -heaved up into hillocks at the Galapagos archipelago. -their fluidity. -with irregular hummocks at Ascension.

Lead, separation from silver.

Lesson, M., on craters at Ascension.

Leucite.

Lime, sulphate of, at Ascension.

Lonsdale, Mr., on fossil-corals from Van Diemen’s land.

Lot, St. Helena.

Lyell, Mr., on craters of elevation. -on embedded turtles’ eggs. -on glossy coating to dikes.

Macaulay, Dr., on calcareous casts at Madeira.

MacCulloch, Dr., on an amygdaloid. -on chlorophaeite. -on laminated pitchstone.

Mackenzie, Sir G., on cavernous lava-streams. -on glossy coatings to dikes. -on obsidian streams. -on stratification in Iceland.

Madeira, calcareous casts at.

“Magazine, Nautical,” account of volcanic phenomena in the Atlantic.

Marekanite.

Mauritius, crater of elevation of.

Mica, in rounded nodules. -origin in metamorphic slate. -radiating form of.

Miller, Prof., on ejected Labrador feldspar. -on quartz crystals in obsidian beds.

Mitchell, Sir T., on bombs. -on the Australian valleys.

Mud streams at the Galapagos archipelago.

Narborough island.

Nelson, Lieut., on the Bermuda islands.

New Caledonia.

New Red sandstone, cross cleavage of.

New South Wales.

New Zealand.

Nulliporae (fossil), resembling concretions.

Obsidian, absent at the Galapagos archipelago. -bombs of. -composition and origin of. -crystals of feldspar sink in. -its irruption from lofty craters. -passage of beds into. -specific gravity of. -streams of.

Olivine decomposed at St. Jago. -at Van Diemen’s land. -in the lavas at the Galapagos archipelago.

Oolitic structure of recent calcareous beds at St. Helena.

Otaheite.

Oysters, extinction of.

Panza islands, laminated trachyte of.

Pattinson, Mr., on the separation of lead and silver.

Paul’s, St., rocks of.

Pearlstone.

Peperino.

Peron, M., on calcareous rocks of Australia.

Phonolite, hills of. -laminated. -with more fusible hornblende.

Pitchstone. -dikes of.

Plants, extinct.

Plutonic rocks, separation of constituent parts of, by gravity.

Porto Praya.

Prevost, M. C., on rarity of great dislocations in volcanic islands.

Prosperous hill, St. Helena.

Pumice, absent at the Galapagos archipelago. -laminated.

Puy de Dome, trachyte of.

Quail island, St. Jago.

Quartz, crystals of, in beds alternating with obsidian. -crystallised in sandstone. -fusibility of. -rock, mottled from metamorphic action with earthy matter.

Red hill.

Resin-like altered scoriae.

Rio de Janeiro, gneiss of.

Robert, M., on strata of Iceland.

Rogers, Professor, on curved lines of elevation.

Salses, compared with tuff craters.

Salt deposited by the sea. -in volcanic strata. -lakes of, in craters.

Sandstone of Brazil. -of the Cape of Good Hope. -platforms of, in New South Wales.

Schorl, radiating.

Scrope, Mr. P., on laminated trachyte. -on obsidian. -on separation of trachyte and basalt. -on silex in trachyte. -on sphaerulites.

Seale, Mr., geognosy of St. Helena. -on dikes. -on embedded birds’ bones.

Seale, on extinct shells of St. Helena.

Sedgwick, Professor, on concretions.

Septaria, in concretions in tuff.

Serpulae on upraised rocks.

Seychelles.

Shells, colour of, affected by light. -from Van Diemen’s land. -land, extinct, at St. Helena. -particles of, drifted by the wind at St. Helena.

Shelly matter deposited by the waves.

Siau, M., on ripples.

Signal Post Hill.

Silica, deposited by steam. -large proportion of, in obsidian. -specific gravity of.

Siliceous sinter.

Smith, Dr. A., on junction of granite and clay-slate.

Spallanzani on decomposed trachyte.

Specific gravity of recent calcareous rocks and of limestone. -of lavas.

Sphaerulites in glass and in silicified wood. -in obsidian.

Sowerby, Mr. G.B., on fossil-shells from Van Diemen’s land. -from St. Jago. -land-shells from St. Helena.

St. Helena. -crater of elevation of.

St. Jago, crater of elevation of. -effects of calcareous matter on lava.

St. Paul’s rocks.

Stokes, Mr., collections of sphaerulites and of obsidians.

Stony-top, Little. -Great.

Stratification of sandstone in New South Wales.

Streams of obsidian.

Stutchbury, Mr., on marine remains at Otaheite.

Subsided space at Ascension.

Tahiti.

Talus, stratified, within tuff craters.

Terceira.

Tertiary deposit of St. Jago.

Trachyte, absent at the Galapagos archipelago. -at Ascension. -at Terceira. -decomposition of, by steam. -its lamination. -its separation from basalt. -softened at Ascension. -specific gravity of. -with singular veins.

Trap-dikes in the plutonic series. -at King George’s sound.

Travertin at Van Diemen’s land.

Tropic-bird, now rare, at St. Helena.

Tuff, craters of. -their breached state. -peculiar kind of.

Turner, Mr., on the separation of molten metals.

Tyerman and Bennett on marine remains at Huaheine.

Valleys, gorge-like, at St. Helena. -in New South Wales. -in St. Jago.

Van Diemen’s land.

Veins in trachyte. -of jasper.

Vincent, Bory St., on bombs.

Volcanic bombs. -island in process of formation in the Atlantic. -islands, their distribution.

Wacke, its passage into lava.

Wackes, argillaceous.

Webster, Dr., on a basin-formed island. -on gypsum at Ascension.

White, Martin, on soundings.

Wind, effects of, on the form of craters.