Emery — Green River Desert Section, Utah. 567 



of dome-like pinnacles so steep sided that they cannot often be 

 scaled by the experienced mountaineer, and separated by narrow 

 clefts which are equally impassible. ' ' 



And again : 



"Standing upon one of the summits of the Henry Mountains 

 and looking eastward I found myself unable to distinguish the 

 Gray Cliff Sandstone by color either from the lower part of the 

 Flaming Gorge Group or from the Vermilion Cliff Sandstone. ' ' 



The distinction of two formations in these massive 

 sandstones is equally as difficult in the Green River 

 Desert as in the Henry Mountain region. As already 

 shown, color in these beds is not a sure ground for the 

 drawing of formational boundaries, and in the absence of 

 fossils I can see no basis for drawing such a boundary in 

 the midst of a series lithologically similar from top to 

 bottom. In my opinion the "Vermilion Cliff" and 

 "Gray Cliff" sandstones constitute a single stratigraphic 

 unit, which is equivalent to the Wingate sandstone of the 

 Xavajo Reservation. This correlation is based on the 

 position of the unit between the Chinle formation below 

 and a series of limestone, shale, sandstone, and gyp- 

 sum beds above which is believed equivalent to the 

 Todilto as mapped by Gregory in the western part of the 

 Xavajo Reservation, and further upon its lithologic 

 character, especially its massiveness and cross-bedding, 

 which duplicate that found in the "Wingate in Arizona. 

 This interpretation differs from that of Gregory, 15 who 

 correlated the Wingate sandstone with only the lower 

 part of the series, the "Vermilion Cliff" portion, and 

 who regarded the Todilto as the equivalent of the less 

 massive zone present in the "Vermilion Cliff" — "White 

 Cliff" series of beds in the High Plateaus. It has been 

 shown above that this less massive zone is not constant in 

 stratigraphic position in Green River Desert, but does in 

 fact occur at various horizons in the series, and is not a 

 formation or definite member of a formation. The pres- 

 ent interpretation differs also from that of Doctor Cross, 

 who in eastern Utah correlated the upper ("White 

 Cliff") portion of the series with the La Plata, 16 and 

 regarded the "Vermilion Cliff" sandstone as older than 

 La Plata. The present interpretation differs also from 



15 Gregory, H. E., op. cit., plate III. 



16 Cross, Whitman, Stratigraphic results of a reconnaissance in Western 

 Colorado and Eastern Utah," Bull. Geol. Soc. America, 15, p. 642, 1907. 



Am. Jour. Sci. — Fourth Series, Vol. XLVI. No. 274.— October, 1918. 

 24 



