158 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



(Page 472.) : 'The general conditions under which correlation of the San 

 Juan formations with those of the Plateau section must be made are as follows. 

 Adjacent to the mountains there is a broad zone of gentle westward slope in 

 which Cretaceous beds occur. The main streams flowing west and south cut 

 valleys into and in some places through the Cretaceous into underlying formations. 

 Nearer the canyon of the Colorado the valleys widen and broad platforms and 

 terraces of Jurassic and Triassic beds appear, the Cretaceous being restricted to 

 the divides and isolated mesas. The Paleozoic formations appear at first only 

 in isolated exposures in the deeper canyons, but far to the southwest rise to form 

 the broad plain called the Colorado Plateau, on the south side of the Grand 

 Canyon. Thus the older the formation the greater are the gaps between districts 

 of good exposures, and the greater the likelihood that in the covered tracts un- 

 suspected complications have entered into the problem." 



(Page 473.) [In 1899, A. C. Spencer made a trip into the Paradox and Sinbad 

 Valleys, where he found below the Dolores] "coarser Red Beds, often conglomer- 

 atic, with pebbles 3 inches or more in diameter, and several hundred feet of such 

 strata were noted. No opportunity was found to measure a section showing the 

 full thickness of these coarser Red Beds, but, as observed by Peale, they are under- 

 lain by fossiliferous Permsylvanian Carboniferous in Sinbad Valley * * *." 



Cross and Howe suggest (page 475) that the lower 514 feet, red sand- 

 stones, of Newberry's generalized section of the valley of the Colorado 

 (Report of Expedition from Santa Fe, New Mexico, to the Junction of the 

 Grand and Green Rivers of the Great Colorado of the West in 1859) is 

 equivalent to the Cutler. 



(Page 477.) [Button referred the lower 450 feet of Newberry's saliferous 

 series to the Permian. This consists of] "'sandy shales, containing gypsum and 

 selenite in abundance, with here and there thin bands of limestone.' At some 

 unspecified horizon in this formation Dutton found ' several specimens of Bake- 

 wellia and an attenuated form of Myalina.' On this ground he correlates these 

 beds with the Permian of the Kanab Canyon district, where Walcott had dis- 

 covered a more extensive fauna. 'The Permian beds are distinguished for their 

 dense and highly variegated colors chocolate, maroon, dark brownish reds 

 alternating with pale, ashy gray, or lavender colors.' 



"The Permian strata thus described are overlain by 'a very coarse, almost 

 conglomeratic sandstone,' some 50 feet in thickness, which Dutton correlates 

 unhesitatingly with the 'Shinarump conglomerate' (a particular conglomerate 

 within the Shinarump group), referring to the fact that it is persistent and uniform 

 in aspect wherever it appears through the plateau country of Utah and Arizona." 



Cross and Howe suggest (page 478) the equivalency of Dutton's Permian 

 and the Cutler, but note that there is no community of species in the under- 

 lying Pennsylvanian Aubrey and Hermosa, thus indicating that though the 

 stratigraphic position is the same, there is no certainty the formations are 

 equivalent. 



The deposits of the upper Paleozoic of west-central Colorado are dis- 

 cussed in the chapter upon the Pennsylvanian beds of the basin region. 



