570 Emery — Green River Desert Section, Utah. 



Of the Jurassic age of the rocks just described there 

 can be no doubt, for it is amply shown by the fossil con- 

 tent. They are lithologically similar to beds referred 

 by Gregory to the Todilto in Piute Canyon and near Nav- 

 ajo Mountain, and like those beds lie between massive 

 Wingate sandstone, below, which is an excellent key 

 formation, and the Navajo sandstone above. Gregory, 

 however, states that the expression of the beds in the 

 northwest part of the Navajo Reservation is so unlike the 

 Todilto of the type locality that the correlation can only 

 be considered a working field hypothesis. 19 So while it 

 is recognized that the beds between the Wingate and Nav- 

 ajo in Green River Desert are the equivalent of similar 

 beds near Navajo Mountain they are referred to the 

 Todilto with a question mark because later work may 

 show that the Navajo Mountain Todilto is not indeed the 

 equivalent of the type Todilto. 



The Todilto ( ?) constitutes the lower part of what Gil- 

 bert termed the "Flaming Gorge group" in the vicinity 

 of Henry Mountains and has been included by Lupton in 

 the McElmo in Grand Count}^ and in Castle Valley. 

 Lupton, however, was aware that the inclusion of these 

 beds in the McElmo might not stand the test of more 

 detailed work than the time at his command and the exi- 

 gences of his examination permitted, for in this connec- 

 tion, quoting a list of fossils found in the limestone men- 

 tioned above, he said : 



; 'As the McElmo formation in its type area is not known to 

 include any marine strata, it is possible that the bed containing 

 this fauna is older than the basal beds of the typical McElmo. ' ' 20 



Navajo Sandstone (Jurassic). 



The Navajo sandstone includes the beds between the 

 Todilto (?) formation and the variegated shale and 

 coarse sandstone and conglomerate of the Salt Wash 

 member of the McElmo. It is broadly exposed in Green 

 River Desert outcropping along San Rafael River and 

 also in the region of the Flat Tops. 



In the field two members of the Navajo sandstone were 

 mapped on lithologic grounds. The lower of these is 

 about 300 feet thick and consists of medium-grained sand- 



19 Gregory, H. E., op. cit., p. 56. 



20 Lupton, C. T., Geology and coal resources of Castle Valley, in Carbon, 

 Emery, and Sevier counties, Utah, U. S. Geol. Survey, Bull. 628, p. 24, 1916. 



