Part 10

Beds 4 to 9 dip at an angle of 45 deg. to the N.N.E.

Our imaginary pit is of course only a sort of geological Juan Fernandez, but it will serve in some degree to illustrate the method of dealing with various rocks and fossils when met with in the field, and how they may best be collected and carried home. A few additional suggestions where to look for fossils may, however, be given here. To begin with, I never neglect to search the fallen masses, especially their weathered surfaces, or to look carefully over the heaps of quarried materials, whatever they may happen to be, piled on the floor of the pit. In working at the beds themselves, remember that fossils frequently occur in layers which of course represent the old sea-bottom of the period; to find these, it is necessary to follow the beds in a direction at right angles to their stratification, till you arrive at the sought-for layers, or zones.

Do not be surprised, when collecting from a formation you have never before studied, if the fossils are not at first apparent, though many are known to be present. The eye requires a few days in which to become accustomed to its fresh surroundings, and when the same spot has been carefully hunted over every day for a week, it is astonishing what a quantity of fossils are discernible where not one in the first instance was recognised.

HOW TO PREPARE THE SPECIMENS FOR THE CABINET.

The first thing to be done on unpacking our specimens is to pick out those which require the least attention, and get them out of the way. These will be your rock specimens, which, if they have been trimmed properly in the pit, will not need much further manipulation; a word or two, however, as to the best method of proceeding when it is desirable to reduce a specimen, will not be out of place. If you wish to divide it in two, or detach any considerable portion, the specimen may, while held in the hand, be struck a smart blow with the hammer; as, however, it not frequently happens that even with the greatest care the specimen under this treatment breaks in an opposite direction to that required, it is advisable to adopt a somewhat surer method, namely, to procure a block of tough wood, and in the centre bore a hole just large enough to receive the shank of the cold chisel, and thus hold it in an upright position with the cutting edge uppermost; placing the specimen on this, and then hitting it immediately above with the hammer, it may be fractured through in any required direction. To trim off a small projection, hold the specimen in your hand with the corner towards you and directed slightly downwards, then with the edge of the striking face of the hammer hit it a smart blow at the line along which you wish it to break off; the object of inclining the specimen is to make sure that the blow shall fall in a direction inclined away from the portion you wish to preserve, a modus operandi which it is necessary to bear well in mind if you would not spoil many a choice specimen. Anything beyond very general directions, however, it is impossible to give in such matters as this: experience, and a few hints from those who have themselves had practice in collecting and arranging specimens, are worth more than any written description, however lengthy and elaborate.

Having reduced your specimen to the required size and shape, the next thing to be done is to write a neat little label for it--the smaller the better--stating, first the nature of the specimen, secondly the geological formation to which it belongs, thirdly the locality from which it was procured, and fourthly the date when acquired, thus--

Limestone. Lower Carboniferous. Quarry, 1 mile N.W. of ---- 21. 8. 8-.

ruling a neat line at the top and bottom (red ink lines give a more finished appearance than black). When the label is dry, damp it to render it more pliant, and gum it on to the flattest available surface of the specimen, pressing it well into any small inequalities that it may hold the firmer. A small quantity of pure glycerine (about an eighth part) should be added to the gum before use, in order to prevent its drying hard and brittle. The specimen is now ready to place in its tray and be put away in the cabinet.

In the next place, pick out the fossils which you obtained from the limestone. With the cold chisel set in its block of wood, and the trimming hammer, remove as much of the surrounding rock (matrix) as you can without damaging the fossil, and with a smaller chisel any pieces that may be sticking to and obscuring it. Fossils in soft limestone, such as chalk, are best cleaned with an old penknife, and needles fixed into wooden handles, and finished off by the application of water with a nail-brush. Should you have the misfortune to break any specimen in the process of trimming, it should at once be mended. The most effectual cement for this purpose is made by simply dissolving isinglass in acetic acid, or, where the specimen contains much iron pyrites, and there would be a danger in starting decomposition, shellac dissolved in spirits of wine. When, however, neither of these are handy, chalk scraped with a penknife into a powder, and mixed with gum to the consistency of a thick paste, answers admirably. Failing this, however, gum alone will frequently suffice.

The next thing is to place the like kinds together in their several trays, writing a label, as before, for each tray, but leaving a blank space at the top for the insertion of the name when ascertained. The commoner sorts may be named from the figures of them given in the text-books (see list at the back of the title page); but failing this, it will be the best plan to seek the help of any friends who have collections, or to take the fossils to some museum, and compare them with the named specimens there exhibited. The label may be laid at the bottom of the tray with the fossils loose on the top of it, each fossil being marked with a number corresponding to one on the label. Another plan is to fasten the label by one of its edges to the side of the tray; or, if the fossils are small and mounted on a piece of card fitting into the tray, it may be gummed with them to the card.

Now let us take the shells we obtained from the dark-blue clay, with those and the bones from the old river bed up above. Gently turn them out of the tins, in which they were packed in the quarry, on to a paper or the lid of a card-board box, and with a pair of forceps pick them carefully out of the bran, and place them in large shallow trays, taking care not to mix those from the different beds. As we found when collecting them, these shells are extremely brittle from loss of animal matter, and our first object is therefore to harden them by some process, so that they will bear handling. To accomplish this you must get a saucepan, one of those wire contrivances for holding eggs when boiling, or a big wire spoon, such as formerly was used for cooking purposes, a packet of gelatine, and some flat pieces of tin, which last are easily procured by hammering out an old mustard or other tin, having previously melted in a gas flame the solder wherewith it is joined. Half fill the saucepan with clean water, and put in as much gelatine as when cold will make a stiff jelly; melt this over the fire, placing the fossils meanwhile in a warm (not hot) corner of the fire-place; then when the gelatine is quite dissolved, pile as many of them, whole or in pieces, into the egg-boiler, or spoon, as it will contain, hold them for a second in the steam, and then lower them gradually into the hot gelatine until it completely covers them. Little bubbles of air will rise and float on the surface. As soon as these cease to appear, raise the fossils above the surface and allow them to drip; then pick them up one by one with the forceps, and spread them out on pieces of tin before the fire, but not too close to it. As soon as their exterior surfaces become dry, and before the gelatine gets hard, they should be taken up (they may be handled fearlessly now), and the superfluous gelatine sticking to the surface gently removed with a camel's-hair brush dipped in clean warm water; otherwise, when dry, they present an unnatural varnished appearance, and have a tendency, on small provocation, to become unpleasantly sticky.

Small bones may be treated in like manner, but for large ones, weak glue is to be preferred to gelatine, which is only suitable for the finer and more delicate objects. Where it is desired to harden only a few things, it is better to mix the gelatine in a gallipot, which can be heated when required by standing it in a saucepan of water on the fire. In any case the gelatine need never be wasted, as it will keep almost any length of time, and can therefore be put by for future use. In default of the egg-boiler or wire-net spoon, an equally useful plan is to make a strainer from a piece of perforated zinc by turning up the edges all around, and attaching copper wire to it by which to lower the fossils into the gelatine, and raise them again.

When the fossils are quite dry they can be sorted, and those which have come to pieces may be mended with diamond cement (i.e. isinglass dissolved in acetic acid), and then properly labelled and placed in trays, or mounted as previously described.

To the plant remains and Lignite there is little that can be done beyond trimming them to suit the trays. Should there be much iron pyrites in the Lignite, it is sure, sooner or later, to decompose, when all that can be done is to throw it away. In the case, however, of valuable fruits and seeds, such as those from the London Clay of Sheppey, it is worth while to preserve them, if possible, in almost the only way known, viz. by keeping them in glycerine in wide-mouthed stoppered bottles, or by saturating them with paraffin.

Having prepared the specimens for the cabinet, the next thing is to arrange them in proper order. There are several ways of doing this, but for those who have not had much experience the following plan will be found the best:--Group the specimens according to the formations to which they belong, and arrange these groups in proper sequence (vide Table, p. 16); then take each group, and arrange the specimens it comprises in columns. Beginning at the top of the left-hand corner, place first the specimens of the rock itself, and under it any examples of minerals, concretions, etc., found in that rock; next the fossil plants, if any; and finally, such animal remains as you have arranged according to their zoological sequence, beginning with the lower forms (vide Table, p. 32). Unless cramped for room, each formation should begin a new box, its name being written on a slip of paper and placed at the head of the columns of trays. A label setting forth its contents should be fixed outside each of the boxes, which can then be put away on your cupboard shelves.

TABLE OF THE PRINCIPAL FOSSILIFEROUS STRATA ARRANGED IN CHRONOLOGICAL ORDER.

Land Plants.-----------+ Invertebrata.--------+ | Fishes.------------+ | | Amphibia.--------+ | | | Reptiles.------+ | | | | Birds.-------+ | | | | | Mammalia.--+ | | | | | | Man.-----+ | | | | | | | | | | | | | | | | | | | | | | | {Alluvial Deposits, | | | | | | | | Quaternary, { River Valley | | | | | | | | or { Gravels and | | | | | | | | Pleistocene. { Cave Deposits. | | | | | | | | {Drift and Glacial | | | | | | | | { Deposits. V | | | | | | | | | | | | | | Cainozoic, {Pliocene. | | | | | | | or {Miocene. | | | | | | | Tertiary. {Eocene. | | | | | | | | | | | | | | { {Chalk. | | | | | | | M { Cretaceous. {Upper Greensand. | | | | | | | E { {Gault. | | | | | | | S { | | | | | | | O { Neocomian. {Lower Greensand. | V | | | | | Z { {Wealden. | : | | | | | O { | : | | | | | I { { {Purbeck. | : | | | | | C, { {Upper.{Portland. | : | | | | | { { {Kimmeridge Clay. | : | | | | | or { { | : | | | | | { { Mid. {Coral Rag. | : | | | | | S { { Oo- { {Oxford Clay. | : | | | | | E { {lites.{ | : | | | | | C { { { {Cornbrash and | : | | | | | O { { { { Forest Marble. | : | | | | | N { Jurassic.{ {Lower.{Great Oolite. | : | | | | | D { { { {Fullers' Earth. | : | | | | | A { { { {Inferior Oolite. | : | | | | | R { { | : | | | | | Y { { Lias. | : | | | | | | : | | | | | { {Trias, or New | : | | | | | P { Poikilitic. { Red Sandstone. V ? V | | | | A { {Permian. | | | | L { | | | | AE { {Coal Measures. V | | | O { {Millstone Grit | | | Z { Carboniferous. { and Yoredale | | | O { { Rocks. | | | I { {Carboniferous | | | C, { { Limestone, etc. | | | { | | | or { Devonian and Old | | | { Red Sandstone. | | | P { | | | R { {Ludlow Beds. | | | I { {Wenlock Beds. | | V M { Silurian. {Woolhope Beds. | | A { {Tarannon Shale. | | R { {Llandovery or May | | Y. { { Hill Group. V | { | { {Bala and | { { Caradoc Beds. | { {Llandeilo Flags. | { {Arenig Group. | { Cambrian. {Tremadoc Slates. | { {Lingula Flags. | { {Menevian Beds. | { {Longmynd and | { { Harlech Group. V { : { Pre-Cambrian and : { Laurentian. ?

NOTES ON THE DIFFERENT FORMATIONS MENTIONED IN THE TABLE.

RECENT.--The alluvial deposits of most river valleys and some estuaries still in course of formation, containing fossil shells and mammals, all of living species.

QUATERNARY, POST-PLIOCENE, or PLEISTOCENE.--1. Including the raised beaches around the coast, the older gravels of river valleys and the cave deposits, in all of which the shells are identical with those living in the rivers and seas of to-day, whilst the animals are many of them extinct, only a few being now found living on the spot.

2. The glacial drifts that cover all England north of the Thames, and which consist of sands, gravels, and clays, full of big angular stones frequently flattened on one side, scratched and sometimes polished from having been fixed in moving ice and forced over other rocks. A very interesting collection of these "boulders," as they are called, can be easily made, for they belong to almost every formation in England, and have some of them been brought from great distances, whilst the number and variety obtainable from a single pit is astonishing.

CAINOZOIC, or TERTIARY.--Beds of this age, in England at all events, are for the most part made up of comparatively soft rocks, gravels, sands, and clays, and are found in the eastern and south-eastern counties. They are divided into--

1. Pliocene, mainly consisting of a series of iron-stained sands, with abundant shell remains, and locally known as "crags." The shells are very partial in their distribution, the beds in places being almost entirely made up of them, whilst in others scarcely one is to be found. The great majority are of the same species as many still living. The Pliocene is subdivided into three groups:--

a. The Norwich Crag Series, sometimes called the "Mammaliferous Crag," as at its base the bones of mastodon, elephant, hippopotamus, rhinoceros, and some deer have been found. The shells in it are such as still abound on the beaches of the eastern coast to-day--whelks, scallop shells, cockles, periwinkles, etc.

b. The Red or Suffolk Crag, its two names indicating its characteristic colour (a dark red-brown) and chief locality. From the base are obtained the celebrated phosphatic nodules miscalled "Coprolites," whence is manufactured an artificial manure, and with them are found the rolled and phosphatized bones and teeth of whales, sharks, etc. Amongst the shells the Reversed Whelks (Fusus contrarius), Fecten opercularis, Pectunculus glycimeris, several kinds of Mactra and Cardium, etc., are the commonest. Walton-on-the-Naze, Felixstowe, and Woodbridge are the best known localities.

c. The White or Coralline Crag is generally of a pale buff colour, and is in places almost entirely composed of the remains of Polyzoa. These (formerly called Corallines, whence the name Coralline Crag) are beautiful objects for a low-power microscope, or pocket lens, and are easily mounted in deep cells on slides. The bits of shell and sand that stick to them should be carefully removed with the point of a needle. A very large number of shells occur in this crag: of bivalves, the Pecten is very abundant, and its valves are frequently thickly grown over with Polyzoa; Cyprina Islandica, Cardita Senilis are also plentiful; and of univalves, the genus Natica is common. The Coralline Crag is best seen in the neighbourhood of Aldborough, Orford, Woodbridge, and other places in Suffolk.

2. Miocene, possibly represented in the British Isles by a small patch of clays and lignites at Bovey Tracey.

3. Eocene, divided into--