PERMO-CARBONIFEROUS OF NORTHERN NEW MEXICO 9g 
most three hundred feet of these exposures, the intervening three 
hundred 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 con- 
formable with the superincumbent and subjacent beds, and doubt- 
less represent the Lower Trias and perhaps more or less of the Upper 
Permian. The section of the bluff herewith given was made oppo- 
site our first camp on the Poleo, about one 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 immediate valley of the Poleo the strata 
dip northward to the walls of the Mesa Prieta; immediately south 
of the creek they dip abruptly southward. About two 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 exclusively of Upper Triassic and superincumbent beds, 
descend to the immediate valley of the Poleo and Capulin creeks. 
The Mesa Prieta rises about fifteen hundred feet above the beds 
of the Poleo and Capulin. Near the middle of the bluffs, at about 
the 8,coo-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 four hundred feet of these 
beds at least, everywhere, their age is assumed simply from their 
color—evidence, to say the least, that is 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 Jurassict and the lighter colored 
sandstones of the Cretaceous all lying quite conformably with the 
Red Beds below. 
About a mile and a half beyond the little settlement called 
« The beds immediately overlying the gypsum have been called Dakota by Darton 
(Bull. U.S.G.S. No. 435) and Shaler (Bull. U.S.G.S. No. 315, p. 262), but without any 
evidence therefor. We searched in these shales for fossils, but without success. 
Elsewhere the beds overlying the Trias are either the marine Sundance (Wyoming), 
the Hallopus beds (Cafion City, Colo.), Morrison (Southern Wyoming), or Lower 
Cretaceous (Kansas). 
