WARD] HISTORICAL REVIEW OF OPINION. 429 



the types bave collectively an aspect so inoderu, that one almost in- 

 stinctively regards them as Tertiary; and yet some of these types are 

 now known to have existed in the Cretaceous and even in the Jurassic 

 period. 



"lu view of the conflicting and silent character, respectively, of these 

 paleontological oracles the following suggestions are offered: It is a 

 well-known fact that we have in North America no strata which are, 

 according to European standards, equivalent with the Lower Creta- 

 ceous of Europe, but that all North American strata of the Cretaceous 

 period are equivalent with those of the Upper ('retaceous of that part 

 of the world. That the Fox Hills group is of Upper Cretaceous age 

 no one disputes, the only question being as to its place in the series. 

 A comparison of its fossil invertebrate types with those of the Euro- 

 pean Cretaceous indicates that it is at least as late as, if not later than, 

 the latest known Cretaceous strata in Europe. If, therefore, that i)ar- 

 allelism is correctly drawn, and the Laramie group is of Cretaceous 

 age, we have represented in America a great and important period of 

 that age which is yet unknown in any other part of the world. Be- 

 sides this, we may reasonably conclude that the Fox Hills group of 

 the West is equivalent with the Upper Cretaceous strata of the Atlan- 

 tic and Gulf coasts, between which and the Eocene Tertiary of those 

 regions there is no known equivalent of the Laramie group. 



" If paleontologists should finally agree upon regarding the Laramie 

 group as of Cretaceous age, it must be because of the continuance of 

 certain vertebrate Cretaceous types to the close of that period, and 

 the presence of mammalian Tertiary types in the strata immediately 

 following; but the following facts, in addition to those which have been 

 already stated, should be carefully considered before any such agree- 

 ment is made : 



"With rare and obscure exceptions no mammalian remains are known ^ji 



in North American strata of earlier date than that of those which were "^ ** ''^'^ 



deposited immeduUely after the close of the Laramie period and upon its 

 strata. Immediately from and after the close of the Laramie period 

 their abundant remains in the fresh-water Tertiaries of the West show 

 that highly-organized mammals exi.sted in great variety and abun- 

 dance; all of which ma\ be i)roperly regarded as constituents of a Ter- 

 tiary fauna, and many of which are by accepted standards of distinct 

 ively Tertiary types. If the presence of these forms in the strata re- 

 ferred to, and their absence from the Laramie strata immediately be- 

 neath them, together with the presence of Uinosaurians there, be held 

 to prove the Tertiary age of the former strata, then was the Tertiary 

 period ushered in with most unnatural suddenness. Sedimentation was, 

 at least in part, unbroken between the Laramie group and the strata 

 wiiich contain the mammalian remains referred to, so that the local con- 

 ditions of the origin of all of them were substantially the same, and 



