2 INTRODUCTION. 



tent upon the peculiar domain of the geologist, and to obtain 

 some knowledge of the origin, composition, and mode of 

 occurrence of the rocks from which Palaeontology derives its 

 materials. Lastly, Palaeontology, apart from its own import- 

 ance as an independent science, is employed by the geologist 

 to assist him in his determination of the chronological succes- 

 sion of the materials which compose the crust of the earth. 

 Palaeontology, therefore, must be separately studied in its rela- 

 tion to historical Geology. 



DEFINITION OF FOSSILS. 



All the natural objects which come to be studied by the 

 palaeontologist are termed " fossils " (Lat. fossus, dug up). In 

 most cases, fossils, or, as they are often termed, " petrifactions," 

 are actual portions of animal or vegetable organisms, such as 

 the shells of Molluscs, the skeletons of Corals, the bones of Ver- 

 tebrate animals, the wood, bark, or leaves of plants, &c. ; and 

 these may be preserved very much in their original condition, 

 or may have been very much altered by changes subsequent to 

 their burial. Strictly speaking, however, by the term "fossil" 

 is understood " any body, or the traces of the existence of any 

 body, whether animal or vegetable, which has been buried in 

 the earth by natural causes " (Lyell). We shall find, therefore, 

 that we must include under the head of fossils objects which at 

 no time themselves formed parts of any animal or vegetable, 

 but which, nevertheless, point to the former existence of such 

 organisms, and enable us to reason as to their nature. Under 

 this head come such fossils as the moulds or " casts " of shells 

 and the footprints left by various animals upon sand or mud. 



In the great majority of cases fossils are the remains of 

 animals or plants which are now extinct that is to say, which 

 no longer are in existence, but have entirely disappeared from 

 the earth's surface. In some cases, however, fossils are the 

 remains of recent animals that is, of animals which are still 

 found in a living condition upon the globe. The term " sub- 

 fossil," sometimes applied to these, has been more appropriately 

 applied in another sense, and is best discarded in this con- 

 nection. The terms " fauna " and " flora " are employed in 

 Palaeontology much as they are by the naturalist, to mean 

 the entire assemblage of the animals or of the plants respect- 

 ively belonging to a particular region or a particular time. 

 Thus we may speak of the " fauna" of the Carboniferous 

 Period, or the "flora" of the Tertiary Epoch, or the fauna of 

 the Chalk, or of any other set of beds. 



