THE RISE AND PROGRESS OF PALEONTOLOGY. 171 



our latitudes, and which are either extinct or exist only in more north- 

 ern climates. Thirdly, in Siberia and in other northern regions of 

 Europe and of Asia, bones and teeth of elephants, rhinoceroses, and 

 hippopotamuses occur in such numbers that these animals must once 

 have lived and multiplied in those regions, although at the present 

 day they are confined to southern climates. The deposits in which 

 these remains are found are superficial, while those which contain shells 

 and other marine remains lie much deeper. Fourthly, tusks and bones 

 of elephants and hippopotamuses are found not only in the northern 

 regions of the Old World, but also in those of the New World, al- 

 though, at present, neither elephants nor hippopotamuses occur in 

 America. Fifthly, in the middle of the continents, in regions most 

 remote from the sea, we find an infinite number of shells, of which the 

 most part belong to animals of those kinds which still exist in south- 

 ern seas, but of which many others have no living analogues ; so that 

 these species appear to be lost, destroyed by some unknown cause. It 

 is needless to inquire how far these statements are strictly accurate ; 

 they are sufficiently so to justify Buffon's conclusions that the dry 

 land was once beneath the sea ; that the formation of the fossiliferous 

 rocks must have occupied a vastly greater lapse of time than that tra- 

 ditionally ascribed to the age of the earth ; that fossil remains indicate 

 different climatal conditions to have obtained in former times, and 

 especially that the polar regions were once warmer ; that many species 

 of animals and plants have become extinct ; and that geological change 

 has had something to do with geographical distribution. 



But these propositions almost constitute the framework of pale- 

 ontology. In order to complete it but one addition was needed, and 

 that was made, in the last years of the eighteenth century, by Will- 

 iam Smith, whose work comes so near our own times that many living 

 men may have been personally acquainted with him. This modest 

 land-surveyor, whose business took him into many parts of England, 

 profited by the peculiarly favorable conditions offered by the arrange- 

 ment of our secondary strata to make a careful examination and com- 

 parison of their fossil contents at different points of the large area 

 over which they extend. The result of his accurate and widely ex- 

 tended observations was to establish the important truth that each 

 stratum contained certain fossils which are peculiar to it ; and that the 

 order in which the strata, characterized by these fossils, are superim- 

 posed one upon the other is always the same. This most important gen- 

 eralization was rapidly verified and extended to all parts of the world 

 accessible to geologists ; and now it rests upon such an immense mass 

 of observations as to be one of the best established truths of natural 

 science. To the geologist this discovery was of infinite importance, as 

 it enabled him to identify rocks of the same relative age, however 

 their continuity might be interrupted or their composition altered. 

 But to the biologist it had a still deeper meaning, for it demonstrated 



