MOOK, STUDY OF THE MORRISON FORMATION 



71 



The Morrison (McElmo) formation is described 

 by Cross (1910, 4) in the Engineer Mountain 

 quadrangle, as follows : 



"In the Engineer Mountain quadrangle the Mc- 

 Elmo has a thickness of 400 to 500 feet. It is here 

 composed more largely of shale than in the Tellu- 

 ride quadrangle, where its thickness on the San 

 Miguel Eiver is nearly 1000 feet and where sand- 

 stone forms its most important element. Shale 

 and sandstone alternate in the formation in vari- 

 able proportions. The beds of shale as a rule are 

 colored some shade of green, but are locally pink 

 or deep Indian red, and they include some varie- 

 gated red and green bands. The shales are fine 

 grained and sandy and occur in homogeneous 

 bands, in places several feet thick, with little or no 

 distinct lamination. The sandstones are fine and 

 even grained and friable in texture; those of the 

 lower portion resemble the La Plata sandstone, and 

 at least one of the upper beds is very similar to the 

 Dakota sandstone. The arenaceous layers are 

 white or yellowish and locally grade horizontally 

 and vertically into sandy shale and thence into clay 

 shale. In the upper part of section there is a fine- 

 grained conglomerate which is practically identical 

 with the lowest conglomerate of the Dakota. The 

 large number of crumbling beds in the formation 

 cause numerous gaps in all discovered exposures, 

 and no detailed section can be given." 



GRAND RIVEE AREA 



The Morrison (McElmo) formation is well ex- 

 posed along the Grand Eiver, from its junction 

 with the Gunnison Eiver westward into eastern 

 Utah. For some distance east of the junction with 

 the Gunnison Eiver it is also exposed in the walls 

 of the canyon of the Grand Eiver. West of Grand 

 Junction, the beds are exposed on the south side 

 of the river only. The exposures are usually sev- 

 eral miles south of the river, and occur partly in 

 the high cliff which forms the northern boundary 









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Fig. 25. — Section' of the 

 Morrison formation, on 

 Dexter Creek, Rico 

 qiiaclranole, Colorado. 



Scale, 125 feet to 1 inch. 

 (Cross.) 



