152 ANNALS NEW YORK ACADEMY OF SCIENCES 



known, are the Washita beds near Canon City, Colorado (Stanton, 1905, 

 11). The npper beds of the Morrison at this locality cannot be later 

 than Fredericksburg in age, but may be much older. In Montana the 

 Morrison is overlain by the Kootenie formation, which contains- Co- 

 manchean plant remains, some of which are represented in the Patuxent 

 formation in Maryland. The Kootenie apparently lies conformably on 

 the Morrison, and it is quite probable that the Morrison and Kootenie 

 are not distinct formations, but belong to the same deposition cycle. 

 This question will be taken up again in considering the evidence from 

 the vertebrate fossils. 



In many areas the Morrison is overlain by the Cloverly, I^akota, or 

 Purgatoire formations, which belong, in whole or in part, to the Co- 

 manchean period. In western Colorado the Morrison is overlain by the 

 Dakota sandstone. The contact with the Cloverly and Purgatoire is 

 often sharp, but there is no evidence of extensive erosion between the 

 two formations. Erosion to a slight extent probably did take place, how- 

 ever. As noted by Lee, the relations of the Morrison to the overlying 

 formations are much closer than to those beneath. 



■ In Texas and adjoining regions, where the Morrison is absent, there 

 is a great development of Comanchean marine deposits. Where the 

 Morrison is present in considerable thickness, the marine Comanchean is 

 absent or is very thin. 



The evidence from the stratigraphic relations indicates, therefore, that 

 for the eastern areas at least, the age of the Morrison is Comanchean 

 rather than Jurassic. 



The evidence from the flora as to the age of the Morrison is not con- 

 clusive, a number of species of cycads comprising the entire known flora. 

 As noted above. Ward placed the age of these as Jurassic. The flora of 

 the overlying formations has more significance and will be considered in 

 connection with the discussion of the evidence from the vertebrates. 



The invertebrate fauna has no value in determining the age of the 

 formation. Most of the genera range from jMorrison to recent time, a 

 few being older. The species also have considerable range and are diffi- 

 cult to determine accurately, owing to poor preservation or lack of dis- 

 tinguishing characters. 



The vertebrate fauna, which is one of the largest and most character- 

 istic vertebrate faunas in any known geological formation, has often been 

 appealed to in connection with the age of the Morrison. Marsh (1878, 

 2) referred the Morrison, or Atlantosaurus Beds, as he called it, to the 

 Jurassic on the basis of evidence from the reptiliaii fauna. Just what 

 this evidence consists in was never published by Marsh. He correlated 



