10 BIOLOGICAL SOCIETY OF WASHINGTON. 



found to characterize the European formations is found in the 

 Cretaceous series of the valley of the Upper Missouri river. 

 Here we have a series of strata which has been held to represent 

 the European Cretaceous series from the Gault to the Upper 

 Chalk, inclusive. In the lower division of this American series 

 there has long been known to exist a flora which, when it was 

 first discovered, was referred by the best authority to the age of 

 the Eocene Tertiary. Even so late as the past year, Mr. J. 

 Starkie Gardner has expressed the opinion that these plants are 

 more likely to be of Eocene age than earlier. Now the strata 

 containing this assumed Tertiary flora are overlaid by a series, 

 several thousand feet in thickness, which contains an abundance 

 of marine tvpes that correspond with those of the Cretaceous of 

 Europe. Indeed, several of the species are regarded as identical ; 

 and the types embrace reptiles, fishes, and coelenterata, as well 

 as all the classes of mollusca. Then, resting upon this series, 

 and its Atlantic border equivalent, we find the whole Tertiary 

 series, at least up to the close of the Miocene. Furthermore, 

 a considerable number of these American Tertiary forms are 

 usually regarded as identical with European Tertiary species. It 

 would thus seem that both the stratigraphical and concurrent 

 paleontological evidence are decidedly against the Tertiary age 

 of that flora, and in favor of its Cretaceous age, notwithstand- 

 ing its homotaxial relationship to the Tertiary flora of Europe. 



The commingling of types in one formation which, in Europe, 

 respectively characterize two or more separate formations, is a 

 matter of not uncommon occurrence in America and other parts 

 of the world. These cases occur where the order of the forma- 

 tions seems to agree well with that of the accepted European 

 standard ; and they apparently merely show that the types re- 

 ferred to began their existence earlier, or continued it later, as 

 the case may be, than they were known to have done in Europe. 

 In the other cases the discrepancies are seen to occur as between 

 marine faunas on the one hand, and land faunas and floras on the 



