DISCUSSION. 



Dr. C. A. White: The Trinity beds, to which Mr. Hill refers as lying at 

 the base of the Comanche series, I have, in a work now in press, provision- 

 ally referred to the base of the North American lower Cretaceous. They 

 contain, besides some undetermined dinosaurian remains, a few species of 

 non-marine mollusca ; but I am at present unable to say whether these forms 

 are more suggestive of Cretaceous than of Jurassic age. 



The fossils which Mr. Hill has exhibited as coming from strata beneath 

 the Comanche, I am at present unable to specifically identify. If they really 

 came from the horizon indicated, I think they represent a hitherto unknown 

 molluscan fauna, and that they are of very great interest. 



I quite agree with Mr. Hill in the opinion that the different subdivisions 

 of the Texan Cretaceous cannot be definitely correlated with subdivisions of 

 the European Cretaceous. I also think that the assumption of such corre- 

 lations as have been published, by various authors both in Europe and 

 America, is much to be deplored, because it retards rather than advances true 

 scientific knowledge. For example, the venerable and distinguished Pro- 

 fessor Roemer, of Breslau, who has published so much upon the fossils of 

 the Texan Cretaceous, and who knows the paleontology of the European 

 Cretaceous as well as any person living, has referred a collection of Co- 

 manche species to the upper Turonian. He does not merely say that the 

 forms which he published are analogous to those of that subdivision of the 

 European Cretaceous, but he refers them definitely to the same, as if it were 

 as clearly recognizable here as in Europe. On the other hand, the Dakota 

 group, after the early claims that its flora indicate Tertiary age subsided, 

 has by common consent among a large number of geologists been regarded 

 as of Cenomanian age. 



Comparatively late investigations have shown that strata equivalent to 

 the Dakota group in Texas not only overlie the Comanche series, but that 

 there is a wide time-hiatus aud unconformity between them ; that is, the 

 assumed correlations, referred to above, place one assemblage of strata far 

 beneath another when in reality its true place is far above. The accom- 

 panying diagramatic table will illustrate the case in hand. 



The right-hand column represents in their order the subdivisions of the 

 European Cretaceous, and the left-hand column those of the general Creta- 

 ceous section of the southern interior portions of North America. The posi- 

 tions of these two portions of the table with relation to each other is not 

 intended to show the taxonomic relation to one another of their respective 



(525) 



