MORRISON SHALES OF COLORADO AND NEW MEXICO 53 
west of Trinidad, Colorado, the sedimentary formations are 
strongly upturned. In some places they are even overturned to 
such an extent that the apparent dip to the west is something 
like 30 degrees. A sharp “hog-back” in this region is locally 
known as the ‘‘stonewall.” The name is derived from a quartz- 
itic sandstone which, on account of its resistance to erosion, 
forms a ridge parallel to the mountain front. The serrate edge 
of this sandstone, which rises in places several hundred feet as 
a sheer wall, forms the crest of this ridge.- This sandstone con- 
tains fossil tree trunks and branches. Stratigraphically above 
the sandstone lies a series of shales and limestones which yield 
fossils of Colorado-Cretaceous type. Beneath the sandstone 
lies a series of shales, sandstones, and limestones, which in turn 
is underlain by an extensive series of red sandstones—the Red 
Beds of the mountain front. Stratigraphically and lithologically 
the ‘‘stonewall’’ is identical with the Dakota sandstone as 
described from various places along the mountain front. This 
stonewall was traced from La Veta, Colo., southward to Gold 
Creek, N. M., a distance of about 4o miles. 
The shale series lying between the Dakota and the Red Beds 
is composed principally of variegated clay-shales, with varying 
amounts of friable sandstones and a few thin seams of impure 
limestone. The best exposed section found is near the town 
of Stonewall, Colo., but no satisfactory place was found for 
making a detailed section, owing to the growth of underbrush 
and to the surface débris. The total thickness, where upper and 
lower contacts could be located, was estimated at 300 feet. The 
shales, sandstones, and limestones of this formation are strati- 
graphically and lithologically identical with those described 
from the canyons to the east and south. They are also identical 
with those described by Mr. Hills from the Walsenburg area a 
few miles to the north. They were identified on the north fork 
of the Purgatory, at the town of Stonewall, and at Gold Creek, 
N.M. There are strong indications that the shale underlies the 
Dakota continuously throughout the length of the region exam- 
ined along the mountains. 
