30 CARBdNIKKROUS FORMATIONS AND FAUNAS OF COLORADO. 



tlu' <^'ool()i4T of llic I'lalcuu proNiiicc as a wliolc, ami liut 75 of the upward of 20U 

 pajifos comprised in it deal directly witii the {geology of the Uinta Mouiitaiiis, and that 

 only of tlie eastern ixirtion. Through his presentation of thesui)ject it thus iiappcns 

 that while the typical exposures of the Red Wall and of the upper and lower Aubrey 

 groups are in northern Arizona, the same names are employed for formations in 

 northwestern Colorado, and that the geologj' of the latter area, historically at least, 

 is intimately connected with that of the Grand Canyon countr\'. In a similar man- 

 ner, since Emmons and King describe the Uinta sediments in connection with those 

 of the Wasatch Mountains, recognizing the same formations and employing the same 

 names in both, the Uinta section can not well be considered apart from that of the 

 W^asatch Mountains. 



1 am especially concerned only with the strata of Carboniferous age in the Uinta 

 Mountains. These are described on page 57 and again on page 146 of Powell's work, 

 while the general section and description for the Plateau province occur on pages 

 ■iO and 5-i. The faunal characters of the Carboniferous are outlined and discussed on 

 pages 76, 79, and 88. 



Over 5,000 feet of strata in the Uinta Mountains are referred by Powell" to the 

 Carboniferous, and four subdivisions of Carboniferous beds are recognized. These 

 are called in ascending order the Lodore group, the Red Wall group, the lower 

 Aubrey group, and the upper Aubrey group. The Lodore group, -1:60 feet in thick- 

 ness, consists of sandstones and shales with conglomerates at the base. The Red 

 Wall group is 3,000 feet thick and consists chiefly of limestones separated by thin 

 sandstones. The lower Aubrey comprises 1,000 feet of rather soft sandstones with 

 intercalated limestones. The upper Aubrey is composed of two members — a massive, 

 homogeneous, light-gray sandstone at the base, called the Yampa sandstone, which 

 has a thickness of 1,000 feet or more, and above 150 to 200 feet of cherty limestone 

 for which the name Bellerophon limestone is employed. 



These four Carboniferous formations are conformable with one another, but 

 according to Powell they are separated by a profound unconformity from the under- 

 Ijnng beds, which have been called the Uinta sandstone. The unconformity is one 

 both of dip and erosion. The diflerence of dip between the Lodore group and the 

 Uinta sandstone is about 1 degrees, the lower formation having the greater inclina- 

 tion to the south. Cliffs of the Uinta sandstone formed prior to the deposition of the 

 Lodore project in some instances iOO feet into the mass of superimposed sediments 

 (page 144). 



The upper Aubrej' formation is succeeded by the Juratrias groups, which 

 received the names of the Shinarump, Vermilion Cliff, White Cliff, and Flaming- 

 Gorge groups. No unconformity was observed between the upper Aubrey and the 



a Powell mentions the constituent members of his Carboniferous series in several places, and each time with a 

 different thickness. The above is the sum of the thicknesses in a detailed section, aggregating in all 5.305 feet. 



