476 CROSS AND HOWE — RED BEDS OF SOUTHWESTERN COLORADO 



ceding pages. Huge fossil bones are commonly reported to occur in 

 these beds and they are supposed to represent the saurian fauna else-, 

 where known in these strata. 



The San Juan valley was partially explored by Holmes (23) and New- 

 berry (33), but there is little profit in trying to recognize the Dolores and 

 Cutler formations in the sections they refer more or less provisionally 

 to the Trias. No fossil-bearing horizon corresponding to the Dolores 

 " saurian conglomerate " was observed by these explorers, although both 

 correlate certain beds with the horizon at which Newberry obtained dino- 

 saur remains farther north, and both refer to this bed as " Triassic (?) " 

 (23, general section, page 244) ; (33, page 105). In his generalized sec- 

 tion Newberry himself calls this fossil- bearing horizon " Jurassic (?)," a 

 reference which seems more reasonable. 



Observations by H. S. Gane. — Important evidence as to the formations 

 of the San Juan valley in Utah has been secured by Dr Henry S. Gane, 

 who in 1897 went from Mancos, Colorado, to the canyon of the Colorado, 

 passing down the San Juan valley on its northern side. Doctor Gane 

 had been my assistant in the Geological Survey during the study of the 

 Telluride and La Plata quadrangles, and was thus well equipped to 

 make correlation studies in the Plateau district. With his permission, 

 I make certain statements of his observations. 



In the San Juan valley the La Plata formation is stated by Gane to 

 have a general development similar to that which it possesses in the 

 lower Dolores valley, according to Spencer. It thickens greatly and its 

 upper and lower sandstone members are very massive, and exhibit red, 

 orange, and yellow colors, though they are often white or gray. The 

 great cliffs and remarkable towers and pinnacles of the valley are mainly 

 caused by the massive La Plata sandstones, and not by Triassic Red 

 beds, as assumed by Holmes and Newberry. Opposite the " Water 

 Pocket fold " the canyon of the Colorado is, according to Gane, mainly 

 cut in the La Plata beds, 1,000 feet or more deep. 



That Gane's correlation is correct, as to the La Plata, is indicated by 

 the presence of the Dolores formation with its fossiliferous limestone- 

 conglomerates below the La Plata. In this conglomerate Gane obtained a 

 large portion of a crocodile jaw, at Clay hill, some 20 miles east of the 

 Colorado and 10 miles north of the San Juan river. This specimen has 

 been described by F. A. Lucas as representing a new form called by him 

 Heterodontosuchus ganei and stated to have marked Triassic affinities 

 (28). It is one of the belodonts, and teeth of these animals are perhaps 

 the most common fossil throughout the limestone conglomerates of the 

 Dolores. Lucas identifies the same species in the Trias of Arizona, as 

 will be brought out later on. 



