HORIZON OF THE MARINE JURASSIC OF UTAH 637 



You will find his discussion of the section in a paper on the Green 

 River Desert section, Utah.'" 



The earliest reference to fossiliferous beds at this horizon in 

 this locality that has come under the notice of the writer is by 

 Gilbert,^ who, in describing the Flaming Gorge formation, says: 

 "In the immediate vicinity of the Henry Mountains it varies little 

 except in color from summit to base, but in other locahties not far 

 distant it is interrupted near the base by thick beds of gypsum 

 and gypsiferous clays, and by a sectile, fossiliferous limestone." 

 Gilbert's Vermilion Clifi and Gray Cliff sandstones in this locality 

 have been generally supposed to represent the two major divisions 

 of the La Plata group, described by Gregory^ in the Navajo country 

 as the Wingate and Navajo sandstones respectively; and although 

 Cross'* interprets the Vermilion Cliff of the older writers to be the 

 upper part, at least, of the present Dolores formation, anyone who 

 has studied the detailed section given by Gilbert in the identical 

 localities from which he describes them cannot help being certain 

 that his upper Shinarump shales are Dolores, and that his Vermilion 

 Cliff sandstone includes the base of the La Plata and probably 

 does not include any of the Dolores. Likewise Gilbert's Gray Cliff 

 is La Plata, and his Flaming Gorge is in part, and probably in 

 totality, the equivalent of the McElmo formation of more recent 

 writers. 



- The present writer has studied these formations in some detail 

 in the region described by Gilbert, particularly along Water 

 Pocket Canyon and on the Water Pocket Flexure. Here the total 

 thickness of the Vermilion Cliff and Gray Cliff together is estimated 

 (not measured) as not less than 1,500 feet. Near the contact 

 between them is about 100 feet of shaly red sandstone, less resistant 

 than the material above and below, and this is beheved by the 

 writer to correspond to Gregory's Todilto beds. The general 



^ Amer. Jour. ScL, XL VI (October, 1918), 551-57. 



^ G. K. Gilbert, Report on the Geology of the Henry Mountains, 1880. 



3H. E. Gregory, "Geology of the Navajo Country," U.S. Geol. Surv., Prof. 

 Paper qj, 191 7. 



''Whitman Cross, "Stratigraphic Results of a Reconnaissance in Western Colorado 

 and Eastern Utah," Jour. Geol., XV (1907), 634-79. 



