LITERATURE 449 



or Pennsylvanian series. These facts show the necessity for the careful 

 study of each district and for due caution in correlation. 



The present paper is primarily a contribution to the knowledge of the 

 Red beds as developed in the San Juan region of southwestern Colorado, 

 and this is accompanied by a partial review of existing literature and 

 such discussion of correlation as seems justified at this time. 



LITERATURE CONCERNING SAN JUAN "RED BEDS" 



Reconnaissance explorations. — The Red beds of the San Juan region 

 received but little attention from the reconnaissance explorers who pre- 

 ceded the geologists of the Hayden Survey. In 1859 J. S. Newberry, 

 with the Macomb expedition, camped on the Animas river a little above 

 Durango, but the only excursion made from that point appears to have 

 been to the south, down the river, and the excellent section of lower 

 Mesozoic and Paleozoic rocks exposed on the river banks for several 

 miles to the north escaped examination by this keen observer. Had 

 Newberry studied with care any section of the Red beds in the Animas 

 valley, we should doubtless have had, thus early, a valuable comparison 

 with the Triassic section of northern New Mexico, where he had discov- 

 ered fossiliferous horizons containing many plants and a number of 

 vertebrates. As it was, Newberry merely noted the fact that " the hills 

 just above our camp are composed of red sandstone and conglomerate 

 (Triassic), very much disturbed " (33 * page 81). 



In 1873 the Animas Valley section was crossed by the Hawn brothers 

 accompanying an expedition under Captain Ru finer and by J. J. Ste- 

 venson, of the Wheeler Survey. The former merely refer to red sand- 

 stones without mention of their probable age, except as shown that they 

 come above fossiliferous Carboniferous strata (of the Hermosa Pennsyl- 

 vanian) (17, page 68). The latter gives a thickness of 1,500 feet to the 

 red strata of the Trias and says that they abut against the Carboniferous 

 (38, page 378) — a statement which we believe can only refer to a rela- 

 tion existing along an east-west fault observed by us east of Engineer 

 mountain. 



The first of the Hayden Survey geologists to observe the San Juan 

 Red beds was F. M. Endlich in 1874. He examined them in the 

 Animas, Dolores, and San Miguel valleys, and refers to their presence 

 in the Uncompahgre canyon, which " is considered inaccessible." End- 

 lich assigns the red strata between the fossiliferous " Middle Carbonifer- 

 ous " (Hermosa) and the " Lower Cretaceous " sandstone [meaning the 

 La Plata, now assumed to be Jurassic] to the " Upper Carboniferous," 

 and states that " Trias and Jura are missing or reduced to a minimum 



♦The numbers refer to the bibliography at the end of this paper. 



