32 CAUHONIKKKOt'S FORMATIONS AND FAUNAS OF COLORADO. 



Between tlie Flaniing (rurge group, with a fiiuiia idontitiod as fi'c.sh-water Juras- 

 sic, and tlio uppei' Aubrey, which is C'arhouiferous, intervene three formations 

 whose age was not ascertained — tli(^ Sliinai'UMij), \'('i'niilion Ciitl'. and White ('lit}' 

 groups. These ix'long to the lied Beds sei'ies and lia\'(' hrcn placrd with tlic .Inr.i- 

 trias. There is some reason to l)ciieve that the upper limit of th(> Carbonifei'oiis 

 should have been placed at a somewhat higher horizon, and it is possible that the 

 upper portion of the Uinta sandstone should have been included in the same period. 

 These points will l)e discussed further on. 



Botli lithologically and faunally the geologic sections in northeastern Utah and 

 northern Arizona are sufKcienth" unlike, so far as the Paleozoic strata are concerned, 

 to cast suspicion upon the correctness of Powell's correlations. The lower Aubrey 

 and Red Wall groups, as described by Powell in the diti'erent sections, seem to present 

 pretty nnich the same lithologic characters, but the upper Aubrej' group is more 

 variable. ■" To the southward, in the Grand Can3'on countrj', these beds are a series 

 of cherty limestones. At the junction of the Grand and Green they are a series of 

 sandstones with intercalated cherty limestones, with a homogeneous sandstone at the 

 summit 1-50 feet in thickness. In the Uinta Mountains we have a homogeneous gray 

 sandstone which we call the Yampa sandstone, from 1,000 to 1,300 feet in thickness, 

 capped by a bed which is believed to be the equivalent of the one mentioned as 

 found at the summit of the series at the junction of the Grand and Green, and 

 varies from 150 to 200 feet in thickness. On the south side of the Uinta Mountains 

 it is an indurated, calciferous sandstone, but on the north side of the mountains it is 

 a cherty limestone, and on both flanks it is characterized by a species of Bellerophon. 

 Here we have called it the Bellerophon limestone." (Page 65.) The Lodore group, 

 which is typically exposed in the eastern Uintas, does not extend far to the south, 

 nor was the Tonto group, which, in the Gx'and Canj^on region, underlies the Red 

 Wall group, traced far to the north. Because of a certain similarity in stratigraphic 

 position Powell wished to correlate these two formations and to employ for both the 

 name Tonto group (page 56). Walcott, however, has shown that the Tonto group is 

 of Cambrian age," while the Lodore group can, with great jirobability, be referred 

 to the Carboniferous.* 



In the Uinta Mountains the Lodore group is underlain unconformablj' by the 

 great mass of the Uinta sandstone, 12,500 feet in thickness, of which the Uinta Range 

 is mainly composed. The age of this series was not ascertained, but it was referred 

 tentatively to the Devonian (page 70). The Uinta sandstone rests uncomformabh- 

 upon the Red Creek quartzite, of which 10,000 feet are reported without the bottom 

 having been seen. 



In the Grand Canyon region, uncomforraablj' below the Tonto sandstone, is found 



I' Am. Jour. Sei., 3d ser., vol. 26, 1883. p. 439. 



'^Powell state.s that Carboniferous fossils have been found in tlie Ludore grroiip (pp. .56 and 117), but apparently none 

 were collected (p. 79). 



