MOOK, STUDY OF THE MORRISON FORMATION 157 



related. Berry gives the correlation of Morrison-Kootenie together ap- 

 proximately equalling the Patuxent-Arnndel. 



Lee (1915, 2) has recently given strong diastrophic evidence for the 

 Comanchean age of the formation. 



The evidence for Comanchean age of the Morrison seems much stronger 

 than that for Jurassic age. The interval between the Sundance and the- 

 Washita is a long one, and the Morrison may not occupy the whole of it, 

 but only the upper portion. It is probable that the Morrison is not of 

 exactly the same age throughout the whole area of its occurrence, and it 

 is very improbable that every particular bed in a given locality necessarily 

 has a corresponding bed in some other locality. Tbe Morrison is the 

 product of a slow accumulation process, and therefore may fill a con- 

 siderable part of the interval between the Sundance and Washita. The 

 most probalile condition is that the greater part of the Morrison is 

 Comanchean in age, with Jurassic members in its lower portion in some 

 areas. It is possible also that in the southwestern areas the base of the 

 Morrison is much lower than in the eastern areas, and may include con- 

 siderable Jurassic. 



OEIGITs^ AND INTEEPKETATION OF THE MOERISON 

 FORMATION 



• Summary of Characters 



In the preceding pages many facts regarding tlie Morrison formation 

 have been recorded. A number of these which may have a liearing on 

 the question of the origin and geologic significance of the Morrison are 

 here briefly summarized : 



1). The Morrison has a very wide distribution. As noted in the sum- 

 mary of the stratigraphic relations of the formation, the area which is 

 now underlain by the Morrison probably covers several hundred thousand 

 square miles, and its original area, before being exposed to the extensive 

 erosion which occurred in the Rocky Mountain region at the end of Cre- 

 taceous time, probably amounted to four or five hundred thousand square 

 miles and perhaps more. 



2). Considering the vast area occupied by the formation, it is very 

 thin. The greatest thickness reported is something like 900 feet, but it 

 is usually very much less than that. 



3). The thickness is variable over large areas, and to a lesser extent 

 in small areas. In the southwestern areas the thickness varies from 400 

 to 900 feet ; in the northwestern areas the actual thickness and variation 

 are both somewhat less ; in the eastern and central Wyoming areas the 



