50 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull.106. 



In several of their joint papers Messrs. Meek and Hayden suggested 

 the correlation of the "lower series" of their section with the Lower or 

 Gray Chalk of the English geologists. In 1861 they stated their views 1 

 thus: 



Having now considered, in the order of their succession, the several rocks em- 

 braced in the lower series of the Nebraska cretaceous deposits * * * it will be 

 interesting to see how nearly their synchronism with known horizons in the Creta- 

 ceous system of the old world can be traced out. With this view we have carefully 

 compared with European forms all the fossils in the several Nebraska collections 

 from the rocks, including those most recently obtained, to which the new species 

 described in this paper belong. These comparisons have satisfied us that the forma- 

 tions under consideration, that is, the Niobrara division, Fort Benton group, and the 

 Dakota group represent together the Lower or Gray Chalk, and probably the Upper 

 Greensand of British geologists (Turonien and Cenomanien of d'Orbigny). 



Seven identical or closely related species are listed as occurring in 

 both the American and the foreign formations. In Prof. Meek's latest 

 work, so frequently 'cited, this correlation is again maintained and based 

 on the same evidence. At that time less than twenty-five species were 

 known to belong to the Colorado fauna. 



A comparison of the much greater number of the species now known 

 with those of the European Turonian in the light of more definite state- 

 ments concerning the vertical range of European species as given by 

 Barrois, 2 Schluter, 3 Zittel, 4 and others furnishes additional evidence 

 mainly in the same direction. The following comparative lists contain 

 the most prominent examples of identity or close similarity : 



From the Colorado formation. From the Cenomanian. 



Nautilus elegans. Nautilus elegans. 



Scaphites warreni. 



•mis. J D 



From the Turonian. 



Exogyra suborbiculata. Exogyra suborbiculata. 



Anomia subquadrata. Anomia truncata. 



Avicula gastrodes. Avicula caudigera. 



Inoceramus labiatus. Inoceramus labiatus. 



Inoceramus deformis. Inoceramus cuvieri. 



Amauropsis bulbiformis. Amauropsis bulbiformis. 



Rostellites dalli. Rostellites elongata. 



Baculites gracilis. Baculites bohemicns. 



Prionotropis woolgari. 5 Prionotropis carolinus. 



( Prionotropis woolgari. 

 Prionotropis lccvianus. Ammonites nodosoides. 



Prionocyclus wyomingensis. Ammonites germari. 



In Germany Dr. 0, Schluter has described, under the name "Em- 

 scher Mergel," a formation overlying the Turonian which he regards as 

 intermediate between that formation and the Senonian, though it has 



» Proc. Acad. Nat. Sci. Phila., 1861, p. 423. 



2 Barrois, C: Terrain Cretace de l'Angleterre, Lille, 1876. 



3 Schluter, C. : Cephalopoden'der oberes deutschen Kreide, Palaeontographica, Vol. xxiy, 1876, pp. 

 87-134. 



* Zittel, 1£. von. : Handbuch dcr Palaeontologie. 



Scaphites larvseformis 



> Scaphites aequalis. 



