Emery — Green River Desert Section, Utah. 557 



also suggested by the apparent absence of the white, 

 petroliferous sandstone described above in a number of 

 places toward the junction of the Grand and Green 

 rivers, for though I did not have the opportunity of 

 examining this area in detail, from a distance it appears 

 that this oil sand is locally absent. 



The sandstone just described underlies the beds re- 

 ferred by Gilbert to the lower member of what he 

 termed the Shinarump group in the Henry Mountains 

 region 4 and which is now known as the Moenkopi forma- 

 tion in the Navajo Country to the south. 5 In the north- 

 ern part of that area the beds directly below the Moen- 

 kopi are known as the Goodridge formation, and from the 

 physical character and sequence it appears likely that 

 this white Pennsylvanian (?) sandstone is equivalent to 

 the top of the Goodridge. The fact that the Pennsylva- 

 nian (?) sandstone is oil-bearing in Green River Desert 

 as is the Goodridge near Bluff on the San Juan River in 

 southern Utah, affords further evidence of the validity of 

 such a correlation. The Goodridge formation in the San 

 Juan field was definitely determined to be Pennsylvanian 

 in age on the basis of fossils collected there by Woodruff. 6 

 A brief examination in the Green River Desert revealed 

 no fossils in the white sandstone, but because of its strat- 

 igraphic position it is here provisionally referred to the 

 Pennsylvanian. 



Moenkopi Formation (Triassic). 



The Moenkopi formation here includes the series of 

 reddish shales and sandstones between the white Penn- 

 sylvanian (?) sandstone below and the Shinarump con- 

 glomerate above, the intervening De Chelly sandstone not 

 being present in this area. The Moenkopi is exposed in 

 the heart of San Rafael Swell and under The Ledge 

 between the Dirty Devil and Green rivers, where it forms 

 the " riser" to the "step" made by the overlying Shina- 

 rump conglomerate. 



The Moenkopi formation is arenaceous throughout. At 



4 Gilbert, G. K., Geology of the Henry Mountains, U. S. Geog. and Geol. 

 Survey of the Terr., p. 6, 1877. 



5 Gregory, H. E., Geology of the Navajo country, II. S. Geol. Survey, 

 Prof. Paper 93, P. Ill, 1917. 



6 Woodruff, E. G., Geology of the San Juan oil field, Utah, U. S. Geol. 

 Survey, Bull. 471, p. 85, 1912. 



