GEOLOGICAL CONTINUITY. 57 



mineral composition to the Cretaceous 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 Maestricht 

 beds of Holland, the Pisolitic Limestone of France, the Faxoe Lime- 

 stone 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 other regions, we do actually meet with strata which have been 

 deposited during the period marking in Europe the interval between 

 the White Chalk and the lowest Tertiary deposits, and which con- 

 tain, therefore, an intermixture of Cretaceous and Eocene types of 

 life. The most celebrated of these transitional formations, so far 

 as known, is the " Laramie Group " of North America, the precise 

 position of which in relation to the strata above and below has been 

 a matter of much controversy. 



We may pause here to consider how it is that we may never hope 

 to find a complete series of deposits linking on one great formation 

 to another, as, for example, the Chalk to the Eocene rocks. In the 

 first place, only a limited portion of the earth has as yet been 

 properly examined, and we have therefore no right to expect that 

 we have as yet hit upon the area, or areas, to which the process of 

 rock-forming was transferred at the close of the Cretaceous period 

 proper in Europe. We have, however, the full right to expect that 

 we shall ultimately find formations which will have to be intercalated 

 in point of time between the White Chalk and the Eocene ; and, as 

 before said, examples of such are already known to us. In the 

 second place, we have every reason to suppose that many of these 

 intermediate deposits have been destroyed at some period subse- 

 quent to their formation by what is technically called " denudation," 

 or, in other words, by the action of rain, rivers, ice, and the sea. 

 In the third place, many of the missing deposits may have been 

 concealed since their formation by the deposition upon them of 

 other newer rocks ; or they may be situated in areas which are at 



