MOOK, STUDY OF THE MORRISON FORMATION 



69 



"Other sections show many changes in the relative development of 

 sandstone and shale at any given horizon. The conglomerate, number 14 

 of section, is similar to the Dakota in character, 

 but is very variable in development. Holmes noted 

 the presence of a conglomerate near the top of his 

 'Lower' Dakota in the plateau country westward, 

 and sporadic developments of the same in the Mor- 

 rison beds may be seen in various places at the 

 base of the Front Kange." Owing to the similarity 

 of the McElmo beds with the Dakota on the one 

 hand and the La Plata on the other, it is difficult 

 to determine the exact upper and lower boundaries 

 of the formation. 



The Morrison (McElmo) in the Eico quad- 

 rangle, according to Cross (1905, 10), is 500 feet 

 or less in thickness. It is composed largely of 

 shales at this point, usually of apple green or dark 

 red color, occasionally variegated red or green. 

 The shales alternate with sandstones in varying 

 proportions. The sandstones are white, even 

 grained, and friable; they often grade laterally 

 into sandy shale and finally into clay shale. 



In the Ouray quadrangle, the Morrison (Mc- 

 Elmo) beds are described by Cross and Howe 

 (1907, 6) as a series of alternating shales and 

 sandstones, which vary in thickness and character. 

 The average thickness in this district is from 500 

 to 700 feet, the maximum being about 800 feet. 

 The shales are varied in color. Green predomi- 

 nates, but in the lower beds reds and browns are 

 conspicuous. Many of the shale beds are fine- 

 grained and porcelain-like, but usually they con- 

 tain sand. Sandstones are numerous, and are 

 usually quartzose, fine-grained, gray and friable. 

 They vary considerably in thickness in short dis- 

 tances, and often show transition to shale or clay 

 beds. The separate sandstone layers seldom ex- 

 ceed 20 feet in thickness. 



The following section of the Morrison (Mc- 

 Elmo) formation is given by Cross and Howe for 

 a locality south of Dexter Creek in the Ouray 

 quadrangle : 



Fig. 24. — Se-tion cf the 

 Morrison formation in 

 the Telluriiie quadran- 

 gle, Colorado. 



Scale, 125 feet to 1 inch. 

 (Cross.) 



