8 S. W. WILLISTON AND E. C. CASE 
From the El Cobre Cafion the expedition turned westward on 
the Chama to the mouth of Cafones creek, and then southwest 
across the Piedra Lumbre Mesa to El Rito, or “branch” of the 
Puerco. The top of this mesa is of Upper Triassic age, and, near 
the base of Mt. Pedernal, which rises several hundred feet above 
the mesa, appears for the first time the heavy layer of gypsum 
marking the upper limits of the Red Beds, or so-called Trias. From 
the top of this mesa a good view of the adjacent country is afforded. 
To the north is the Mesa de los Viejos, with the Chama apparently 
occupying a fault line between, and the Arroya Seco in a valley 
formed by the basal Upper Trias rocks sloping from the brim of the 
Cobre Cafion on the east and the superincumbent Triassic rocks on 
the west. To the west lie the Mesa Prieta and the smaller Capulin 
Mesa, separated by the Puerco, Chama, and Capulin streams, whose 
courses seem to have been influenced strongly by the faulting and 
dipping of the Trias. 
The Puerco to the mouth of the Poleo has cut down into Permian 
strata, which attain their greatest exposure on the Poleo about 
one mile from its mouth. Our first camp was made on the Poleo 
(Arroya de Agua), about one mile above its confluence with the 
Puerco.!. Near the junction of the two creeks there is a steep walled. . 
cliff of Permian rocks about a hundred feet in height, with a more 
or less flat table-land above it a mile or so in extent separating it 
from the Trias above. Farther west, where the Permian rocks 
find their greatest exposure, and where the Baldwin quarry is, 
from which so many of the fossils in the Yale collection came, the 
very steep bluffs, in many places so steep as to be unclimbable, are. 
about seven hundred feet in height, composed of alternating red 
sandstones and clays, with white and purple sandstones, clays, and 
conglomerates at the upper part, corresponding quite to the mas- 
sive sandstones forming the brim of the Cobre Cafion, and which 
form the top of the Mesa Poleo, dipping northward to the foot of 
the Mesa Prieta. Phytosaur 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 lower- 
«This Puerco creek is not the one which gave origin to the name of the Puerco 
formation, a stream by the same name farther to the southwest. 
