CORRELATION OF FORMATIONS 477 



Limestone conglomerate was found by Gane widely distributed in the 

 San Juan valley, carrying saurian and crocodilean teeth and bone frag- 

 ments, fossil wood, and ill-preserved shells of Unio. He made no meas- 

 urement of the thickness of the Trias and had no opportunity to study 

 the underlying formation. 



While Gane observed no unconformity between the Dolores and La 

 Plata formations, it is noteworthy that the fossiliferous beds of the 

 Dolores occur near the top of the formation, and that there is here, appar- 

 ently, no massive, vermilion-colored sandstone, like that which is the 

 normal upper member. It is not improbable that this sandstone was 

 largely or wholly eroded before the La Plata deposition. 



THE ZUNI PL ATE A U, NEW MEXICO 



The development of the Triassic and Jurassic formations to'the south 

 from the Colorado area can not be traced so satisfactorily as to the west 

 in the Dolores and San Juan valleys. 



For more than 100 miles south from the La Plata mountains the Red 

 beds and the overlying Jurassic formations are concealed by Cretaceous 

 strata. They reappear, however, in the Zuni plateau, on the western 

 border of New Mexico, and form the surface of a large part of eastern 

 Arizona, both regions being within the Plateau province. 



Newberry traversed this district with the Ives expedition in 1858, and 

 in his report distinguished two groups of strata between the fossiliferous 

 Carboniferous (Pennsylvanian) and the Cretaceous, namely, a lower 

 group variably designated as the "Red sandstones/' "Saliferous sand- 

 stones," or the " Salt group," and the overlying " variegated marls " 

 (33). This simple division Newberry applies all the way from the Little 

 Colorado to Santa Fe, remarking repeatedly that he sees no reason for 

 further subdivision. 



A much more instructive analysis and description of the section of the 

 Zuni plateau was given by Dutton in 1886 (10). He refers the " varie- 

 gated marls " of Newberry to the " Jurassic " and calls them the " Zuni 

 sandstones." The " Saliferous sandstones " of Newberry's report Dutton 

 divides into three formations. At the base is a formation 450 feet thick, 

 mainly " sandy shales, containing gypsum and selenite in abundance, 

 with here and there thin bands of limestone." At some unspecified hori- 

 zon in this formation Dutton found " several specimens of Bakewellia and 

 an attenuated form oiMyalina" On this ground he correlates these beds 

 with the Permian of the Kanab Canyon district, where Walcott had dis- 

 covered a more extensive fauna. " The Permian beds are distinguished 

 for their dense and highly variegated colors — chocolate, maroon, dark 

 brownish reds alternating with pale, ashy gray, or lavender colors " (10). 



