MOOK, STUDY OF THE MORRISON FORMATION 115 



feet; in east-central New Mexico the Morrison varies from 200 to 400 

 feet; and in the canyons of eastern Colorado the thickness is about 200 

 feet. 



There is thus a thinning out towards the north, northeast and especially 

 towards the east. 



LITHOLOGIC CHAKACTEES 



Coarse material occurs throughout the formation, but is much more 

 abundant and in much thicker beds in the western areas than in those 

 farther east. Fine material occurs throughout the formation and com- 

 prises the largest and most typical element in it, but is not usually 

 abimdant near the base. 



VAEIABLE CHAKACTEE OF SECTIONS 



Sections of the Morrison formation, taken in different areas, present 

 both similarities and differences. Most sections contain alternating series 

 of banded or variegated clays or grits and heavy sandstones, with occa- 

 sional thin limestone beds. No single stratum, however, continues for 

 long distances, so far as the conditions are known. A bed of sandstone 

 a certain number of feet from the base in one section may die out and 

 not be represented in another section, or may disappear and another sand- 

 stone take its place. Lee has used the term "uniformly variable'^ for the 

 Morrison beds, a term which fits Morrison conditions veiy well. 



The significance of these features will be discussed in the section on 

 the interpretation of the formation. 



STEUCTUEE AND PETEOGEAPHY 



Steuctueal Featuees of the Moeei«on Foemation" 



Several structural features are often met with in the Morrison, which 

 have considerable significance in regard to the question of the origin of 

 the formation. Among these are cross-bedding, of both stream and wind 

 types, lense-shaped cross-section of beds, and distinct channeling. 



The stream type of, cross-bedding, or cross-bedding in one direction 

 with the inclined beds resting on flat surfaces, is seen throughout the 

 formation in many places. It occurs on a large scale and also on a small 

 scale. Usually the discordance of dips is not very great. 



The wind type of cross-bedding, or cross-bedding at various angles and 

 directions, with the inclined beds resting on curved surfaces, is also seen. 

 It has been noticed near Canon City in the vicinity of the Marsh-Hatcher 



