[33] A liquid, called "Neuber's liquid glue," is an excellent cement for this purpose: it is sold at No. 54, New Oxford Street, London.
When the bones are tolerably perfect, but dry and friable from the loss of their animal oil, they may be made durable by saturating them with drying oil, and exposing them to a considerable degree of heat; in this manner the magnificent skeletons of the sloth tribe, the Megatherium, and Mylodon, in the Hunterian Museum, were prepared. When a bone appears as if cracked into numerous pieces before its removal, but still preserves its form, the only method by which it can be successfully extracted, is by spreading over it a thick layer of plaster of Paris, which should be used of the consistence of cream; when it sets, (which, if the plaster be recently prepared, will be in the course of a few minutes,) the specimen may be carefully extricated, and the plaster removed or not, according to the nature of the fossil, and the parts to be displayed. The bones of the large reptiles which occur in the Wealden and Oolite, may be restored in the same manner. These remains are generally very brittle, and when imbedded in hard grit cannot be extracted whole: they will often fall to pieces on the slightest blow of the hammer or chisel. When of moderate size, it is best not to attempt their removal from the stone, but to trim the block into a convenient shape, and carefully chisel away the surrounding part, so as to expose the essential characters of the bone. In all cases this is an excellent method where practicable, for such specimens have a double interest; they are at once illustrative examples of the fossil, and of the rock in which it was deposited.
But many specimens will not admit of this method; and with large ones it is inconvenient and undesirable, except where bones lie in juxtaposition. The large examples in Tilgate grit, (figured in the Fossils of Tilgate Forest,) were all extracted piecemeal from the rock: and most of the gigantic bones of the Iguanodon, &c. now in the British Museum, were originally in many hundred pieces, and were cemented together with glue in the manner above described; I have found no other method so convenient and effective.
When a bone is too imperfect to be united as a whole, it may be imbedded in Roman cement, or plaster of Paris, which when dry may be coloured of the prevailing tint of the rock. For large heavy specimens, the cement is preferable; it is of easy application, and the fissures and cracks of the bones may be filled up with it, taking care first to cover the parts with thin hot glue, or the cement, when it dries, will shrink and fall out. A thin coating of mastic varnish will restore the colour, and by excluding the air, tend to preserve the specimens.
The teeth have generally undergone the same changes as the bones with which they are associated. The teeth of elephants or mammoths that are imbedded in loose calcareous earth, like the loam and chalk-rubble of Brighton cliffs, and of Walton in Essex, are friable, and apt to split and separate in the direction of the vertical plates of dentine and bone: the pieces should be glued together, and when set, the tooth be thoroughly saturated with thin glue, used very hot, and the superfluous cement removed with a sponge wrung out as dry as possible from boiling water. If there be any portion of the jaw attached to the teeth, it must be carefully preserved; and search should be made for fragments of the articulations, or parts of the joints and sockets.
In argillaceous strata, as the Lias-shale, London Clay, &c., the fossils are frequently saturated with brilliant pyrites, or sulphuret of iron; a mineral which decomposes upon exposure to the atmosphere, and occasions the destruction of the specimens. The fossils of the Isle of Sheppey are peculiarly obnoxious to this change.
FOSSIL ANIMAL REMAINS.
The remains of vertebrated animals in the Lias, very often occur as skeletons more or less perfect, the entire configuration of the original being preserved in many instances (Bd. pl. 7. Petrifactions, p. 340). But the deposit in which they lie is generally laminated, and the shale flakes off without great care; much time, labour, and practice are therefore required, to obtain specimens of any considerable size. To the late Miss Mary Anning, of Lyme Regis, the merit is due, of having first accomplished this difficult task; Mr. Hawkins has subsequently carried the art to perfection, as may be seen in the marvellous examples of Ichthyosauri and Plesiosauri, in the British Museum.[34]
[34] Petrifactions, Room IV. chap. iv. pp. 341, 376.
The small specimens, such as the detached paddles, groups of vertebræ and ribs, &c., that are likely to come under the collector's notice in his personal researches, are not difficult of preservation. Mr. Hawkins employed a strong watery solution of gum arabic as the cement, and plaster of Paris as the ground, using shallow wooden trays of well-seasoned wood, in which the specimens were permanently imbedded: the bones, scales, &c. were then varnished with a solution of mastic, and the ground coloured bluish grey, to imitate the Lias. I have had considerable practice in the dissection of skeletons imbedded in Lias, and having found the method previously described answer every purpose, have not employed that recommended by Mr. Hawkins.