568 Emery — Green River Desert Section, Utah. 



that of Lupton, who in the course of a study of the Cre- 

 taceous beds in Castle Valley and again in Grand County 

 near Greenriver, also briefly examined the underlying 

 rocks and reached the conclusion that the massive 

 Jurassic sandstones ("Vermilion Cliff" and "Gray 

 Cliff") represented the entire La Plata group. 17 



Todilto (?) Formation (Jurassic). 



The rocks here called Todilto (?) formation constitute 

 the middle portion of the La Plata group and comprise a 

 heterogeneous and extremely variable series of shale, 

 sandstone, limestone, and gypsum, but is a perfectly defi- 

 nite unit between the "Wingate sandstone below and the 

 Navajo sandstone above. It is broadly exposed in Green 

 Eiver Desert just east of San Rafael Eeef, and again 

 back from the canyon of Green Eiver and The Ledge. 



The Todilto ( f) formation, characterized by its extreme 

 variability, which is in fact diagnostic, in places appears 

 as an unbedded jumbled mass of reddish shales associ- 

 ated with dirty gypsum and irregular bunches of massive 

 sandstone, as in the Dugout Creek area about 8 miles 

 above the mouth of San Eaf ael Eiver, but elsewhere 

 comprises a series of regularly bedded shales, sand- 

 stones, limestone, and gypsum, as for example, along 

 Green Eiver south of San Eafael Eiver and in places 

 along San Eafael Eeef. The formation varies from 100 

 to about 300 feet in thickness. 



Near San Eafael Eeef where the Todilto (?) is rather 

 regularly bedded a persistent blue-gray, compact lime- 

 stone 2 to 4 feet thick lies from 12 to 15 feet above the 

 base of the formation. This limestone is very fossil- 

 if erous and in a collection made with the assistance of Dr. 

 Harvey Bassler along the Greenriver-Hanksville road 2 

 miles south of Straight Wash the following species have 

 been identified by Dr. T. W. Stanton, who states they are 

 marine invertebrates of Jurassic age : 



Ostrea strigilecula White Gervillia ( f) sp. 



Camptonectes sp. Trigonia quadrangular is 

 Camptonectes stygius White Hall and Whitfield 



PUcatula sp. Cyprina (?) sp. 



17 Lupton, C. T.j Oil and Gas near Green Eiver, Grand County, Utah, 

 U. S. Geol. Survey, Bull. 541, p. 125, 1914. 



