CORRELATION OF SECTIONS 38o 



these are freshwater beds containing an abundance of dinosaur life, a few 

 fishes, turtles, and crocodiles, together with the cycads and petrified wood. 

 This series has long been called the Freshwater Jurassic and, by the late 

 Professor Marsh, Atlantosaurus beds. Various opinions have been held 

 as to the exact position these should be referred to, but it has usually 

 been conceded that they are Jurassic. Professor Scott a few years ago 

 conditionally referred them to the Lower Cretaceous, but in a recent 

 letter to me considered them Jurassic. 



The lower half of the Sioux fault and Freezeout sections is also very 

 similar, and had the fauna of the two localities been carefully collected 

 the similarity would be more marked. These beds are marine and con- 

 tain a fauna of both vertebrate and invertebrate, many species of which 

 are new to science and have not been described. They have been called 

 the marine Jurassic and also designated as the Baptanodon beds ; * a 

 better term would have been Belemnites beds. The Marine series were 

 not found at Red mountain. 



Grouping of the Jurassic 



its DIVISIONS 



In grouping the Eastern Rocky Mountain Jurassic there are but two 

 distinct divisions to consider, although there are local and unimportant 

 developments between the two stages. In the Freezeout hills there are 

 great lenses of white sandstone that sometimes attain a thickness of 25 

 or more feet. 



COMO STAGE AND ITS FOSSILS 



The freshwater beds have already been named the Como stage by Pro- 

 fessor Scott.f This stage may be denned as follows : A formation that 

 is beneath the sandstone and conglomerates of the Dakota stage and is 

 composed of marls, clays, and sandstones, the marls and clays varying 

 in color from drab to maroon with occasional yellowish bands. These 

 are separated by thin bands of light colored sandstone and limestone and 

 occasionally there are bands of calcareous sandstone containing chert 

 and chalcedony. Usually the Como stage is about 200 feet in thickness, 

 sometimes attaining 250 feet and decreasing to 150 feet. Associated with 

 the marl beds are the following fossils : 



* See Marsh : Am. Jour. Sei., vol. xvii, 1870, p. 86, Sauranodon being preoccupied was replaced 

 with Baptanodon. 

 fSee W. B. Scott : Introduction to Geology, p. 477, footnote. 



