48 INTRODUCTION. 



It is perfectly clear that the process of rock-deposition 

 which was going on in Europe towards the close of the 

 Cretaceous period was not, and could not be, abolished by 

 the elevation of the European area, and the obliteration of 

 the Cretaceous sea, but was simply transferred to some other 

 area. In this particular case, we do not happen to know 

 where the new area of deposition may have been. It is 

 quite certain, however, that in whatever area the Cretaceous 

 animals took refuge, there rocks must have been deposited 

 in course of time, as they are in all seas, though it does not 

 in the least follow that the rocks of this new era should have 

 the smallest likeness in mineral composition to the Creta- 

 ceous sediments. If we should at any time discover these 

 rocks, it may pretty safely be predicted what we should 

 find in them in the way of fossils. We should find, namely, 

 some Cretaceous species, probably unchanged ; with these 

 there would be forms allied to the Cretaceous species, but 

 differing from them to a greater or less extent ; in addition, 

 there would be a certain proportion of forms of life wholly 

 unknown in the Cretaceous rocks ; and lastly, there would 

 be a conspicuous absence of certain characteristic species of 

 the Chalk period. In other words, such deposits as we have 

 been speaking of would contain an assemblage of fossils more 

 or less intermediate in character between those of the true 

 Cretaceous period and those of the lowest Tertiary beds 

 (Eocene), which rest upon the Chalk, or they would present 

 an intermixture of Cretaceous with Eocene types. In point 

 of fact, we have fragments of such intermediate deposits (in 

 the Maastricht beds of Holland, the Pisolitic Limestone of 

 France, the Faxoe Limestone of Denmark, and the Thanet 

 Sands of Britain), and we find in them traces of such an 

 intermixture. Moreover, when we come to examine the 

 boundary -line between the Cretaceous and Tertiary in a 

 region far removed from Europe namely, in North America 

 we find that between these two formations, so widely sep- 

 arated in the Old World, we have some four thousand feet 

 of strata (the so-called " Lignitic Series ") containing such 

 a complete intermixture of the forms of life characteristic of 

 these two periods, that it has been a matter of lively con- 



