496 CROSS AND HOWE — RED BEDS OF SOUTHWESTERN COLORADO 



the evidence of the Triassic vertebrate fauna at numerous points, certain 

 correlations are more or less clearly indicated. 



a. The Hermosa formation appears to occupy the same stratigraphic 

 position as the Aubrey of Utah and Arizona. Further investigations are 

 necessary, however, to explain certain faunal differences or dissimilarities 

 noted by paleontologists between the formations. 



b. The Cutler formation, being older than the Ouray unconformity, is 

 probably of Paleozoic age and corresponds more or less closely to the 

 Permian portions of the stratigraphic sections of the Plateau and Missis- 

 sippi Valle}^ provinces. 



c. The Dolores formation includes diminished equivalents of the 

 Shinarump and Vermilion Cliff formations of the Plateau. The Shina- 

 rump may include important divisions not represented in the Dolores- 



d. The La Plata formation is seemingly equivalent to the White Cliff 

 sandstone. Its local assumption of red color has led to confusion with 

 the Vermilion Cliff in certain districts and a reference to the Trias. 

 Since the White Cliff sandstone underlies marine Jurassic beds, and the 

 La Plata transgresses the Dolores and all older beds in marked uncon- 

 formity, the Jurassic age of the lower division of the Gunnison group 

 seems established. 



e. The McElmo formation appears to correspond closely to the Morri- 

 son and Como beds and the Flaming Gorge group of Powell. It is 

 probable that the marine Jurassic horizon belongs between the La Plata 

 and McElmo formations. 



List of Publications cited 



1. Cope, E. D. Monographs, TJ. S. Geographic and Geological Surveys west of the 



100th Meridian, vol. iv, part ii. Report upon the extinct vertebrata obtained 

 in New Mexico by parties of the expedition of 1874, 1877. 



2. Cross, Whitman. Pikes Peak folio, U. S. Geological Survey, Geologic Atlas of 



the United States, folio 7, 1894. 



3. . Telluride folio, U. S. Geological Survey, Geologic Atlas of the United 



States, folio 57, 1899. 



4. . La Plata folio, U. S. Geological Survey, Geological Atlas of the United 



States, folio 60, 1899. 



5. Cross, Whitman, and Spencer, A. C. "Geology of the Rico mountains, Colo- 



rado." U. S. Geological Survey, Twenty-first Annual Report, part ii, pages 

 15-165, 1900. 



6. Cross, Whitman, and Howe, Ernest. Silverton folio, U. S. Geological Survey, 



Geological Atla3 of the United States, folio 120, 1905. 



7. Darton, N. H. " Comparison of the stratigraphy of the Black hills, Big Horn 



mountains, and Rocky Mountain Front range." Bulletin of the Geological 

 Society of America, vol. 15, 1904. 



8. Button, C. E. " Report on the geology of the high plateaus of Utah." U. S. 



Geographical and Geological Survey of the Rocky Mountain region, 1880. 



