TRIASSIC. 513 



In the San Juan Valley, in southeastern Utah, the La Plata sandstone (Jurassic) 

 as identified by Gane is in part red and has been mistaken for Triassic. It is 

 underlain by the fossiliferous limestone conglomerate of the Dolores formation 

 (Triassic). ^^^« 



The Zuni Plateau, in western New Mexico, comprises Permian, Triassic, and 

 Jurassic strata, according to Button.^"'* Cross ^^^^ comments on Button's divisions 

 and finds correlatives with the formations distinguished in Colorado. 



Comparing the formations of the Zuni Plateau, as described by Dutton, with those of 

 southwestern Colorado, it seems probable that the Zuni sandstones represent the Gunnison 

 group. Button's section is not sufficiently detailed to permit a suggestion as to the exact 

 equivalents of the La Plata and McElmo formations, but it is difficult for me to suppose that 

 the Navajo Church is constituted of anything but one of the La Plata sandstone members. 



The Wingate sandstone corresponds in position and character to the upper, vermihon- 

 colored sandstone of the Dolores formation. The absence or subordination of cross-bedding 

 and the constancy of the red color both tend to support such a correlation. If the Wingate is 

 upper Dolores, it would appear probable that the "lower Triassic" of Dutton is at least approxi- 

 mately the equivalent of the lower Dolores, and it may well be that the basal conglomerate 

 called the Shinarump by Dutton is actually the same as the basal conglomerate of the Dolores. 

 Dutton does not speak of Umestone conglomerates in the Trias, nor did he find fossil remains 

 in it, except the abundant fossil wood. 



Regarding northeastern Arizona, Cross ^^^^ says : 



From the Zuni Plateau a wide tract of upland stretches for 150 miles or more northwest 

 to the brink of the Colorado Canyon. On the northeast is the San Juan Valley and on the 

 southwest is the Little Colorado. It is the land of the Moqui and the Navajo Indians. Beneath 

 the Eocene and Cretaceous strata of the higher central plateau appear the Jurassic and Triassic, 

 beds, the character of which on the San Juan side has already been considered. That the same 

 systems are represented continuously from the Little Colorado to the Zuni Plateau was long ago 

 ascertained by Newberry, though definite evidence of the Triassic age of any particular strata 

 has been but recently brought to light. 



In the paragraphs following the one just quoted Cross refers to vertebrate 

 fossils from northeastern Arizona which had been identified by Lucas. ^^^' *'^ The 

 stratigraphic data relating to this area are taken from Ward,^^^ and concerning 

 them Cross ^®^' says : 



The vertebrate fauna discovered by Ward occurs near the middle of a section some 3,500 

 feet in thickness, all of which is assigned to the Trias. Ward divides this section into three parts. 

 At the base are the "Moencopie beds," 700 feet in thickness consisting chiefly of dark reddish- 

 brown soft laminated argillaceous shales, nearly destitute of silica (quartz), highly charged with 

 salt and gypsum. Some calcareous beds grade into white impure limestone. No fossils were 

 found in the Moencopie beds, and Ward states that "the whole series, wherever the contact can 

 be found, always rests in marked unconformity upon the underlying Paleozoic rock (Upper 

 Aubrey)." 



Succeeding the Moencopie come 1,600 feet of variable strata called by Ward the Shinarump. 

 Within this he distinguishes two formations, each 800 feet thick, the lower being the "Shina- 

 rump conglomerate" and the upper the "Le Roux beds." 



The Shinarump conglomerate of Ward is by no means all conglomeratic. His concise 

 characterization is as foUows: "Conglomerates and coarse cross-bedded sandstones, with clay 

 lenses interstratified with gray argillaceous shales and variegated marls." In fact, the marls 

 become locally most prominent in zones which are elsewhere strongly conglomeratic. 

 48011°— 12 33 



