424 C. R. Keyes — Triassic System in New Mexico. 



In western New Mexico, in the Zuni uplift, there exist, as 

 was first shown by Dutton,* similar conditions, except that 

 the evidences of unconformities have not as yet been noted, 

 and in fact no attempt has yet been made to look carefully for 

 them. Between the two lithologically different parts of the 

 Zuni section of the Red Beds there also exists an important 

 conglomerate which the author just mentioned correlates with 

 Powell's Shinarump conglomerate of the Grand Canyon, and 

 which is considered the base of the Triassic of that district. 



According to all available data, derived from the biologic 

 contents, which at best are rather meager, the stratigraphic 

 relationships, and lithologic characters, there is a lower portion 

 of the Red Beds belonging to the so-called Permian (Carbon- 

 iferous) and an upper portion which appears to be Triassic in . 

 age. 



One great difficulty which has been encountered in the con- 

 sideration of the Red Beds in the southwestern United States 

 has been the existence of a great erosion interval during Early 

 Cretaceous times when the Reel Beds suffered severely from 

 planing off during the period when they constituted part of a 

 vast land area. "This fact has only lately been fully appre- 

 ciated, f and its full significance grasped. 



The three general sections ' of western, central and eastern 

 New Mexico may be paralleled as in the subjoined table : 



General, Bed Beds Sections in New Mexico. 



Western Section. Central Section. Eastern Section. 



Dakota sandstones.. Dakota ss. Dakota sandstones ._ 



Wanting • Wanting Comanche sandstones 300 



Zuni shales 1200 Wanting Pyramid shales 100 



Wingate sandstones 800 Wanting Amarillo sandstones 200 



Shinarump shales ._ 1500 Wanting Endee shales__ 300 



Moencopie shales 500 Wanting Cimarron shales 1000 



Madera limestones . Madera li. Not exposed 



The geographic distribution of the Triassic beds presents 

 some special points of interest. East of the Rio Grande the 

 Carboniferous part of the Red Beds probably greatly predom- 

 inates over the Triassic portion. West of that stream the lat- 

 ter no doubt has very much the larger section. Owing to exten- 

 sive erosion that took place over the Red Beds district, at least 

 throughout much of what is now New Mexico, before the 

 deposition of the Dakota sandstone, a large portion of the Tri- 

 assic portion must have been removed. It may be that part 

 of this erosion took place just prior to Triassic times, as the 

 conglomerate bed 500 feet above the base of the Red Beds 



*U. S. Geol. Sur. , Sixth Ann. Kept., p. 135, 1886. 

 fThis Journal (4), vol. xviii, pp. 3(50-362, 1904. 



