40 CROSS 



huge dinosaurs. The flora of the Fort Union group now known to 

 Mr. Knowlton embraces about 500 species. 



The discovery of the Fort Union flora in association with the 

 vertebrate fauna of the Hell Creek beds raises several highly impor- 

 tant questions, such as the relative value of plants and dinosaurs in 

 determining the age of the Fort Union. A discussion of these ques- 

 tions and a comparison of the Fort Union, Shoshone and Laramie 

 floras will be given in a forthcoming paper by Mr. Knowlton. 



The Shoshone flora known to Mr. Knowlton now embraces about 

 300 speecies, 200 of which occur in the Arapahoe and Denver beds. 

 The known flora of undisputed Laramie beds of Colorado contains 

 80 species. It is sufi&cient to say here that the Shoshone flora is 

 distinctly intermediate in character between those of the Laramie 

 and Fort Union and is easily distinguished from either, according 

 to Mr. Knowlton. 



The invertebrate fauna of the Laramie contains both fresh and 

 brackish water forms. The latter belong to Osirea, Corbula, Cor- 

 bicula, Anomia, etc., and are identical with or nearly related to forms 

 also known in brackish water deposits of the Montana group, as at 

 Coalville, Utah, and Point of Rocks, Wyoming, and in Judith River 

 beds. Such forms are rarely found, I believe, in the Shoshone beds; 

 so rarely that there must arise in each case a query as to the signifi- 

 cance of the presence of these forms. Does it necessarily imply a 

 subsidence permitting a recurrence of brackish water conditions, or 

 may the forms in question have adapted themselves to fresh water 

 environment ? The intimate association of brackish and fresh water 

 forms above the Laramie may well raise the latter question in any case. 



The remarkable vertebrate fauna occurring in beds referred to 

 the Laramie in a general way by paleontologists has until recently 

 been a hindrance rather than a help to the stratigrapher engaged in 

 studying the geologic development of the Rocky Mountain region at 

 the close of the Mesozoic era. During the years in which Marsh 

 was engaged in describing in rapid succession the wonderful horned 

 dinosaurs and associated forms "from the Laramie of Colorado," 

 Wyoming, or Montana he came to speak of the "Ceratops beds" 

 and the "Ceratops fauna" collectively, minimizing almost to the 

 degree of ignoring, the importance of stratigraphic and other evidence 

 showing that the vertebrates he grouped together so closely came 



