TRIASSIC PORTION OF SHINARUMP GROUP 99 



fossiliferous lower strata of the Dolores have also been traced down 

 the San Juan Valley nearly to the Glen Canyon of the Colorado, 

 below the Henry Mountains. 



While nothing similar to the Dolores fossiliferous conglomerate 

 has been described from the original area of the Shinarump Group 

 in Utah or Arizona, the discovery by Ward (26) on the Little Colorado 

 River of the vertebrate fauna characteristic of the Dolores shows 

 plainly that a correlation of great importance is to be anticipated when 

 the requisite studies have been made. 



In the literature of geological investigation in the Plateau Province, 

 which is almost wholly of reconnaissance character, a certain bed or 

 zone of strata in many widely separated localities has been called "the 

 Shinarump conglomerate" and its identity in those places asserted. 

 This has been done without much descriptive detail and chiefly on the 

 basis of lithologic character. Now in the Dolores formation the 

 lower zone, embracing all beds found to be fossiliferous, has also a 

 most perfectly diagnostic lithologic phase. This is found almost 

 invariably at the base of, and irregularly developed through, 200 or 

 300 feet of beds. Those who have worked in the San Juan region 

 have come to apply the convenient field term "saurian conglomerate " 

 to this diagnostic phase because one seldom searches in vain in it for 

 teeth or bone fragments belonging to dinosaurs or to belodont crocodiles . 



The peculiar lithologic feature of the "saurian conglomerate" 

 is that it consists mainly of small round gray limestone pebbles, in 

 many places almost pisolitic in appearance, though never showing 

 the structure of true pisolite spheres, and rarely reaching one inch in 

 diameter. The conglomerate is most irregularly distributed, with 

 cross-bedding structure, through sandstone ledges from a few inches 

 to perhaps thirty feet in thickness. The color of conglomerate-bearing 

 ledges is often greenish gray and shales or sandstones of the same 

 tones are common between them. More complete descriptions of 

 the conglomerate zone are given in the Telluride and Rico folios 

 (I and 3). 



The upper part of the Dolores formation is of very variable thick- 

 ness in the San Juan region, owing in all probability to erosion in the 

 ensuing epoch. It thickens westward and has been confidently corre- 

 lated with the Vermilion Cliff sandstone of the Plateau Province (4) . 



