14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



tains, described by G. K. Gilbert, may correspond £0 the Wingate or 

 Lower La Plata and the limestone above the Gray Cliff to the Todilto 

 on the one hand and the marine Jurassic on the other. Equivalents 

 of other formations seem to occur here, as shown in figure 2. They 

 are described by Powell, Dutton, and others, as exposed continuously 

 in the canyon walls northward as far as the Uinta Mountains. 



Emery 1 recognized these subdivisions near Greenriver, Utah, 

 where he correlates the marine Jurassic rocks with Todilto and the 

 overlying sandstone with Gregory's Navajo and the upper sandstone 

 of Cross' La Plata. These beds were both included in the McElmo 

 by Lupton. 2 Still higher in the section is the conglomeratic Salt 

 Wash member and overlying variegated beds. These contain fossil 

 dinosaurs which seem to correlate them with the Morrison 

 formation. 



The occurrence of gypsum in this region above the supposed 

 equivalent of the Navajo (see also the Castle Valley section, fig. 4, 

 p. 17) is not easily explained unless there were two incursions of the 

 Jurassic sea (see p. 27). 



In northwestern Colorado, south of the Uinta Mountains, a similar 

 section has been described by Gale, 3 who correlated the rocks below 

 the variegated beds with La Plata and with White Cliff, 4 describing 

 them as consisting, like the original La Plata, of two sandstones of 

 equal thickness separated by shale. Marine fossils were found within 

 the upper sandstone and also above it. The variegated beds are pre- 

 sumably the same as those from which the collectors for the Car- 

 negie Museum secured dinosaurs of the Morrison type. 



Schultz 5 has more recently examined the sedimentary rocks 

 upturned around the Uinta Mountains, including those formerly 

 examined by Gale. He measured a section near Flaming Gorge 

 north of the mountains, and one at the eastern end of the Uintas in 

 northwest Colorado. In both of these sections there are beds equiva- 

 lent in character and position to the Morrison. Also in both there are 

 beds several hundred feet thick between the Morrison and the marine 

 Turassic (Twin Creek) which may correspond to the Upper sand- 

 stone of the La Plata group. The cross-bedded sandstone (Nugget) 

 below the Twin Creek obviously corresponds to Gale's White Cliff 



1 Emery, W. B., Paper in preparation. 



2 Lupton, C. T., U. S. Geol. Survey Bull. 541, PP- H5-I33, IQ-H- 



3 Gale, H. S., U. S. Geol. Survey Bull. 340, 1008. 



4 Gale, H. S., U. S. Geol. Survey Bull. 415, P- 51, iQio. 

 6 Schultz, A. R., Unpublished manuscript. 



