BESUME OF UTBEATXJRE. 51 



geologic time scale is extremely unfortunate. Yet he seems to think that these names 

 may have some vicarious significance in a palentologic sense, for he says: "The first 

 of the following groups mentioned, however, is not to be here regarded as distinct- 

 ively Subcarl)oniferous, although it may be so in fact, so far as anj^thing is known to 

 the contrary.'' (Page 35.) To understand this last expression in connection with 

 what has gone bef ore^ it is necessary to bear in mind the belief held by this author that 

 the Carboniferous divisions of Mississippian, Pennsj'lvanian, and- Permian are not 

 characterized bj' faunal differences as in the Mississippi Valley. Later paleontologic 

 research, however, seems to substantiate the theorem that throughout the United 

 States these three periods are distinguishable, where present, by characteristic 

 faunas, and that these faunas, where in the same basin, are characterized in the main 

 bj' the same assemblages of the same species as occur in the Mississippi Valley, and 

 where in different basins, bj' assemblages of similar species. 



GRAND RIVER REGION. 



The great Carboniferous outcrop of the Uinta Mountains, with its outliers in 

 Junction Peak and Yampa Peak, is described in the reports of White, Powell, and 

 King, which have just been discussed. To the southeast of this, and separated by 

 beds of Mc'sozoic and Tertiary age, occurs another large Cai'boniferous area of very 

 irregular outline, which is seen chiefly along the valleys of White and Grand rivers 

 and their afliuents. The southern part of this area is formed by the "peninsula" 

 of the Elk Mountains, which is connected with the lai-ger mass by a more slender 

 Carboniferous outcrop along the western flank of the Archean Sawatch Mountains. 

 For convenience this can be denominated the Grand River region, from the stream 

 which divides it almost in the middle. As defined in a previous paragraph, however, 

 the Carboniferous outcrops of the Elk Mountains do not form part of the Grand 

 River region. 



The mountain r(!gion of central Colorado has been visited b}^ many geologists 

 and its geology described in a general or detailed manner, as the case might be, many 

 times. Reconnaissance surveys were made by Peale, Holmes, Hayden, Marvine, 

 and others of the Hayden survey, and by Stevenson of the Wheeler survey, and as 

 it has become the scene of vast and varied mining enterprises it has been the subject 

 of moi-e detailed investigation by the United States Geological Survey in such works 

 as the Leadville and Aspen monographs and the Tenmile and Anthracite-Crested 

 Butte folios, and of man}- minor reports. The sections established in the four 

 works last mentioned, from their detailed and accurate character, and because 

 the constituent strata are grouped upon lithologic or fossil evidence into named 

 formations according to modern usage, can conveniently be taken as sections of 

 reference in the different areas in which the}- occur. The Crested Butte section 



