42 CROSS 



correlation of Black Buttes and Converse County beds suggested by 

 the similarity of their freshwater faunas and the floras. ^^ 



Barnum Brown correlates the Converse County and Hell Creek 

 beds on the basis of unconformable relations to marine Cretaceous, 

 lithologic character, vertebrate and invertebrate fauna, flora, and 

 position relative to Fort Union beds. He also calls them " Post- 

 Laramie" and extends the correlation to the Denver beds because 

 of the Triceratops fauna in the latter.-^ The Triceratops is described 

 by Hatcher and Lull as the most highly differentiated form of the 

 horned dinosaurs known. It was apparently the last of the race. 



The mammals associated with the Triceratops fauna in Converse 

 County, whose Jurassic affinities were so strongly emphasized by 

 Marsh, must manifestly be studied as to their relations to the 

 forms of the Torrejon and Puerco, before their significance can be 

 determined. 



The facts recited seem to me to indicate clearly that when the 

 distribution of fossils of all kinds in the Laramie and several Shoshone 

 formations is more completely known and the phylogeny worked 

 out, it will be found that each formation has its distinctive fauna and 

 flora which can be utilized with certainty in correlating newly dis- 

 covered deposits of obscure relations. 



In the preceding discussion I have avoided the question as to the 

 age of the Shoshone beds, whether Cretaceous or Eocene. I desire 

 now to urge their reference to the Eocene. The Denver beds were 

 originally referred by me to the Eocene, but the great weight attached 

 to the Mesozoic affinities of the vertebrate fauna by paleontologists 

 led to a tentative acquiescence in the assignment of the Arapahoe 

 and Denver formations to the Cretaceous, in the Denver monograph. 

 In that volume I reviewed various aspects of the question and can 

 add but little to what was there said. The main point seems to be 

 that the Laramie and Shoshone beds belong to a transition series 

 between the Cretaceous and Eocene and that whatever break occurs 

 between any two formations is possibly bridged over by deposits of 

 some other locality. The Laramie is related to the Judith River 

 and other brackish water formations of the IMontana Cretaceous, 



"'Stanton and Knowlton, Bull. Geol. Soc. Amer., Vol. VII, 1S98. 

 ^^ The Hell Creek Beds of the Upper Cretaceous of Montana. Bull. Amer. 

 Mus. Nat. Hist., Vol. XXIII, 1907, pp. 823-845. 



