4 PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



quite to the massive sandstones forming the brim of El Cobre Canon and the 

 top of the Mesa Poleo, dipping northward to the foot of the Mesa Prieta. Phy- 

 tosaur bones were found at the base of this white sandstone and in the pebbly 

 conglomerates immediately underlying them. Permian fossils were found only in 

 the lowermost 300 feet of these exposures, the intervening 300 feet of more or less 

 vertical red clays and sandstones here, as everywhere else in the Rocky Mountain 

 region, being quite barren. These rocks lie here, as elsewhere, apparently quite 

 conformable with the superincumbent and subjacent beds, and doubtless repre- 

 sent the Lower Trias and perhaps more or less of the Upper Permian. The sec- 

 tion of the bluff herewith given was made opposite our first camp on the Poleo, 

 about a mile from the mouth of the creek; as is the case with the section at El 

 Cobre, it can be depended upon only for a short distance on either side ; the strata 

 often change abruptly from sandstones to clays and vice versa. 



On the north side of the adjacent valley of the Poleo the strata dip northward 

 to the walls of the Mesa Prieta; just south of the creek they dip abruptly south- 

 ward. About 2 miles above the mouth of the creek the beds bend down sharply 

 and disappear beneath the alluvial deposits of the creek bed, doubtless indicating 

 the line of a fault. Beyond this point the walls of the Mesa Prieta, formed exclu- 

 sively of Upper Triassic and superincumbent beds, descend to the adjacent valley 

 of the Poleo and Capulin creeks. 



The Mesa Prieta rises about 1,500 feet above the beds of the Poleo and 

 Capulin. Near the middle of the bluffs, at about the 8,000-foot line, there is a 

 heavy bed of gypsum, which is taken to be the upper limits of the Trias, though, 

 as we have said, in the entire absence of all fossil remains through 400 feet of these 

 beds at least, everywhere, their age is assumed simply from their color — evidence 

 that is, to say the least, exceedingly dubious, the more so from the fact that there 

 is no petrological distinction between the Trias and Permian. Above this gypsum 

 layer are the brownish and purplish shales of the Jurassic* and the lighter-colored 

 sandstones of the Cretaceous, all lying quite conformably with the Red Beds below. 



Section II. POLEO CREEK. 



Gray sandstones, mostly even-grained with pebbly con- F««t- 



glomerates and shales below. Phy tosaurs 30 Upper Trias 



Softer gray sandstones, weathering into sand 30 ? 



Sandy clay, with beds of thin black shale; plant remains, 



fossil wood 40 Upper Trias? 



Sandy clay, black and green 13 Lower Trias? Barren 



Purplish sandy clay 6 " " 



Coarse yellow sandstone 33 " " 



Loose gray sand 6 " " 



Green and purplish sandstones 3 " " 



Gray and purplish sandstones 13 " " 



Hard clay, variegated and jointed (clifls) 3 " " 



Purplish sandstones and red clay 30 " " 



Loose white sand with beds of red clay 40 " " 



First red nodular layer 6 " " 



Soft fine-grained, light red sandstones, cross-bedded, forming 



tops of pyramids and clifls 6 " " 



Soft fine-grained, light red sandstones, cross-bedded with 



lighter bands of pebbles 3 " " 



Second red nodular layer, with clay 3 " " 



Red clay 2 



Coarse cross-bedded sandstones 6 " " 



Third red nodular layer 6 " " 



Red cross-bedded sandstones 13 Lower Trias? Barren 



• The beds immediately overlying the gypsum have been called Dakota by Darton {Bull. U. S. G. S. 

 No. 43S) and Shaler {Bull. U. S. G. S. No. 31$, p. 26*). We searched in these shales for fossils, but without 

 Buccew. Elsewhere the beds overlying the Trias are either the marine Sundance (Wyoming), the Hallopus 

 beds (Cafton City, Colo.), Morrison (southern Wyoming), or Lower Cretaceous (Kansas). 



