THE PLAINS PROVINCE 107 



Baker and Bowen, describing the Front Range west of the Glass Moun- 

 tains, say that after the Gaptank was deposited the sea "withdrew from the 

 region, subaerial erosion followed, and a resubmergence brought about the 

 deposition of some 8,000 feet of Permo-Carboniferous sediments. This 

 epoch of marine deposition was twice interrupted by uplift which brought 

 about renewed erosion, as is indicated by two unconformities and basal 

 conglomerates in the Permo-Carboniferous series." 



Both of these papers give detailed accounts and sections with lists of 

 fossils showing the marine conditions in the Trans-Pecos Texas region during 

 what the authors call the Permian (?) or Permo-Carboniferous time. In 

 the opinion of the author of this paper the correlation of the Leonard with 

 the Clear Fork and the Word with the Double Mountain must await more 

 proof than is contained in Udden's paper. There is the possibility that they 

 were formed in the same interval of time, or the Clear Fork and Double 

 Mountain may have been formed in the long period represented by the 

 erosion interval described by Baker and Bowen between the Gaptank and 

 the series of limestones above it. 



D. THE LATE PALEOZOIC IN THE NORTHERN PART OF THE PLAINS 

 PROVINCE AND ON THE EASTERN FRONT OF THE ROCKY 



MOUNTAINS. 



On page 62 of Publication 207 of the Carnegie Institution the author 

 has given a resume of the general lie of the Permo-Carboniferous Red Beds. 

 As was shown in that publication, there is a merging of limestone into red 

 shales and sandstones in the northwestern portion of the Plains Province 

 similar to the merging which occurs in Kansas, Oklahoma, and Texas. 



The red beds in the North and on the slopes of the eastern face of the 

 Rocky Mountains have never been placed exactly in the geological column. 

 This is in part due to the lack of determinant fossils and in part due to the 

 conditions of deposition, terrestrial deposition prevailing and producing 

 overlapping and interlocking lenses of relatively small areal extent. More- 

 over, there is little doubt that the "red beds conditions" extended in time 

 from late Pennsylvanian into, if not through, Triassic time. It is, so far, 

 impossible to correlate any of these beds with the more definitely determined 

 beds in Oklahoma or Texas, but there is no question that at approximately 

 equivalent intervals of time similar results were produced on the borders, 

 at least, of the Plains Province by similar conditions. 



The age of the red sandstone and shale has been variously reported by 

 different authors. A portion of the discussion quoted in Publication No. 

 207 of the Carnegie Institution is repeated here to show the attitude of 

 various writers: 



"In Professional Paper 32, United States Geological Survey, Darton discusses 

 the character of the Red Beds of the Front Range of the Rocky Mountains. The 



