THE SCOPE OF PALEONTOLOGY. II 



rupted by gaps, which not only bear a large proportion to our 

 solid information, but which in many cases are of such a nature 

 that we can never hope to fill them up. 



Fossils. — The remains of animals or vegetables which we 

 now find entombed in the solid rock, and which constitute the 

 working material of the palaeontologist, are termed "fossils,"* 

 or "petrifactions." In most cases, as can be readily under- 

 stood, fossils are the actual hard parts of animals and plants 

 which were in existence when the rock in which they are now 

 found was being deposited. Most fossils, therefore, are of the 

 nature of the shells of shell-fish, the skeletons of coral-zoophytes, 

 the bones of vertebrate animals, or the wood, bark, or leaves 

 of plants. AH such bodies are more or less of a hard consist- 

 ence to begin with, and are capable of resisting decay for a 

 longer or shorter time — hence the frequency with which they 

 occur in the fossil condition. Strictly speaking, however, by 

 the term " fossil " must be understood " any body, or the ti-aces 

 of the existence of any body^ whether animal or vegetable, which 

 has been buried in the earth by natural causes " (Lyell). 

 We shall find, in fact, that many of the objects which we have 

 to study as "fossils" have never themselves actually formed 

 parts of any animal or vegetable, though they are due to the 

 former existence of such organisms, and indicate what was the 

 nature of these. Thus the footprints left by birds, or reptiles, 

 or quadrupeds upon sand or mud, are just as much proofs of 

 the former existence of these animals as would be bones, 

 feathers, or scales, though in themselves they are inorganic. 

 Under the head of fossils, therefore, come the footprints of 

 air-breathing vertebrate animals ; the tracks, trails, and bur- 

 rows of sea-worms, crustaceans, or molluscs ; the impressions 

 left on the sand by stranded jelly-fishes ; the burrows in stone 

 or wood of certain shell-fish ; the " moulds " or " casts " of 

 shells, corals, and other organic remains ; and various other 

 bodies of a more or less similar nature. 



FossiLiSATioN. — The term " fossilisation " is applied to all 

 those processes through which the remains of organised beings 

 may pass in being converted into fossils. These processes are 

 numerous and varied ; but there are three principal modes of 

 fossilisation which alone need be considered here. In the first 

 instance, the fossil is to all intents and purposes an actual 

 portion of the original organised being — such as a bone, a shell, 

 or a piece of wood. In some rare instances, as in the case of 

 the body of the Mammoth discovered embedded in ice at the 

 mouth of the Lena in Siberia, the fossil may be preserved 

 * \.2X. fossus, dug up. 



