LITERATURE 451 



similar to Catopterus gracilis. One small gasteropod shell was found and 

 several apparently determinable species of plants were obtained. Unfor- 

 tunately, these fossils, which had been submitted by Mr Hills to paleon- 

 tologists for determination, were lost before a final report upon them was 

 made. The remains were found near the top of the Red bed section of 

 the San Miguel valley, within 100 feet of the white Jurassic sandstone. 



Work of the United States Geological Survey. — A systematic study of the 

 San Juan mountains and adjacent territory for the purpose of folio 

 mapping began in 1895, in the Telluride quadrangle, and is still in 

 progress. Previous to the field work of the past season the Red Bed 

 section had been examined in the San Miguel, Dolores, and Animas 

 valleys and in the La Plata mountains, covering the entire area where 

 the section is exposed on the west and south slopes of the San Juan 

 mountains, excepting a small district east of the Animas river. The 

 results of these investigations as to the Red beds have been published in 

 the Telluride (3) and La Plata (4) folios and in a report on the Geology 

 of the Rico mountains (5), by Cross and Spencer, and will now be 

 summarized. 



During the Telluride work the fossiliferous horizon in the San Miguel 

 valley, discovered by Hills (20, 21), was easily found, and it has been 

 identified, lithologically or by fossils, throughout the area thus far exam- 

 ined, wherever the Red Bed section is complete. In the study of the 

 Rico mountains invertebrate fossils were found in the lower 300 feet of 

 the Red beds, a fauna very closely allied to that in the underlying Car- 

 boniferous formation. This discovery was made before the Telluride 

 folio was issued in 1899. The character of the sedimentary section in 

 the La Plata mountains was also known before that time. 



In the Telluride folio the entire Red Bed section of that quadrangle 

 was referred to a single formation, the Dolores, with the statement that 

 the section was known to be incomplete, and with an allusion to the 

 lower fossil-bearing Rico formation. The Dolores formation was defined 

 as follows : 



"It is desired to apply the name Dolores to the Triassic strata of southwestern 

 Colorado and of adjacent territory so far as a direct correlation may prove to be 

 practicable." 



After reference to the known Triassic fossils and the extent of the sec- 

 tion assigned to the Dolores in the Telluride folio, the provisional nature 

 of this assignment was pointed out in these words : 



" Whether or not all the beds now associated in the Dolores formation are really 

 of Triassic age remains to be determined by further discoveries." 



The Red beds are again referred to the Dolores formation in the La 



