MOOE, STUDY OF THE MORRISON FORMATION 43 



Hogback, which extends all along the western border of the Bocky Moun- 

 tains in Colorado. The river canyon exposures of the Morrison are also 

 widespread. They occur in the canyons of streams east of the Eocky 

 Mountains, such as the Huerfano, Purgatoire, Cimarron and Apishapa; 

 in the canyons of the McElmo, Dolores and other rivers in western and 

 southwestern Colorado ; and in central Montana. 



Other outcrops occur as combinations of hog-back and canyon ex- 

 posures, such as at Canon Cit}^, Colorado; as local surface rock, such as 

 in southeastern Colorado (see distribution map), and near Grand Junc- 

 tion, Colorado; and in the erosion of local anticlines, such as Como Bluff 

 in south-central Wyoming, and in faulted masses, such as the Sioux Fault 

 exposure in Wyoming. 



Purpose and Scope of the Present Work 



The purpose of the present paper is to interpret the Morrison forma- 

 tion, if possible, in regard to age, origin and paleophysiography. It is 

 also desired to give a summary of the present knowledge, so far as it is 

 available in the literature, together with some new field observations. 



Among the problems which have been connected with the Morrison 

 formation is that of its age. Some writers have held that it is Jurassic, 

 and others that it is Comanchean. Still others have held that it is both 

 Comanchean and Jurassic. It is desired to show that the Morrison is 

 essentially Comanchean, but that some portions of it, especially in the 

 western areas, may possibly be Jurassic. 



Various opinions have been held regarding the origin of the Morrison. 

 It has been considered marine, lacustrine, fiuviatile and combinations of 

 these. An attempt will be made in the present paper to show that the 

 Morrison is essentially a broad alluvial plain, formed of coalescing alluvial 

 fans, and possibly a true delta in the southeastern areas. It must have 

 been deposited under conditions somewhat similar to those now existing 

 in the great alluvial plains in eastern China. 



The fauna and flora are listed for purposes of reference and summary. 



STRATIGRAPHY 



Morrison Formation in Eastern Colorado and New Mexico 



general 



The Morrison formation outcrops along the front of the Rocky Moun- 

 tains in Colorado in a nearly straight line, from the Wyoming border to 

 New Mexico, and south in New Mexico to a jDoint a few miles south of 



