488 CROSS AND HOWE RED BEDS OF SOUTHWESTERN COLORADO 



whole (43, page 27). This opinion seems based mainly on the dis- 

 covery by Howell, in 1874, of a supposed marine Jurassic fauna in the 

 lower part of theShinarump group, in southern Utah (36, pages 80,81). 

 In fact, the fossils obtained by Howell belong, as I am informed by T. W. 

 Stanton, to the Permian fauna reported by Walcott (39) from Kanab 

 valley, and which was also found by the Fortieth Parallel geologists in 

 the Wasatch mountains and by them called Permo-Carboniferous (24). 

 This mistake in regard to Howell's collection seems to have been largely 

 responsible for the idea long prevalent with many geologists, that the 

 Jura and Trias of the western United States belonged to one system. 



CORRELATIONS WITHIN TEE ROCKY MOUNTAIN PROVINCE 



Difficulties of the correlation. — The Red Bed section of the mountainous 

 portion of Colorado and Wyoming is clearly not divisible into the units 

 traceable throughout the Plateau province. The evident general reason 

 for this is that the intervals of orogenic disturbance and erosion preced- 

 ing and following the Triassic sedimentation were here much more pro- 

 ductive of stratigraphic breaks than in the Plateau area. There is much 

 evidence of these effects cited by the Hayden Survey geologists, and even 

 more is indicated on the Hayden geological maps of Colorado. Further- 

 more, the changes in lithologic character in the mountain province are 

 much more notable and render correlations less certain. So great is the 

 variance between the sections exposed in different parts of the mountains 

 that an attempt to review the literature in detail would go far beyond 

 the limits which must be assigned to this discussion. Until many dis- 

 tricts have been reexamined with care, it will be premature to attempt 

 direct correlation of the Dolores and Cutler formations as such with the 

 elements of sections in central and northern Colorado; but there are 

 various facts bearing on the distribution of Triassic and Carboniferous 

 Red beds which may be briefly presented. 



Fossiliferous Trias on Red Dirt creek. — The presence of fossils in the Red 

 beds on Grand river, some 130 miles north of Ouray, was announced by 

 R. C. Hills (20) in 1880, in the note calling attention to the fossiliferous 

 Trias of the San Miguel river, the Dolores formation. Red Dirt creek, 

 where Hills found a " bone bed " resembling that of the San Juan region, 

 is some 12 miles above the mouth of Eagle river and heads on the eastern 

 side of the White River plateau. 



About 20 miles farther north the Hayden map (19) represents the 

 Trias as overlapping the edges of Paleozoic beds and coming in contact 

 with the Archean rocks of the Park range. Whether this relation is due 

 to the pre-Dolores disturbance and erosion remains to be proven, but it 

 seems entirely reasonable to suppose that it may be of that origin. 



