EXTENT OF THE CRETACEOUS FORMATION. 107 
even here they exhibit characters sufficient to distinguish them from any rocks we had before 
met with. 
It will be remembered that I have suggested that the high white mesa seen north of the 
Moqui villages is composed of this series of Upper Cretaceous strata. 
LAS VEGAS TO THE CIMARRON. 
Throughout the entire interval of two hundred miles between Las Vegas and the crossing of 
the Cimarron, with the exception of occasional sheets or masses of trap, and a small basin of 
fresh water Tertiary strata, the only rocks seen belong to the Cretaceous formation. In this 
region the streams are generally more or less cafioned, and the exposures of the underlying 
rocks are frequent and full, showing that beneath the more modern materials an unbroken sheet 
of Cretaceous strata occupies a belt of this width. We shall see hereafter that the crossing of 
the Cimarron is by no means the eastern limit of this formation, but that, except when covered 
by Tertiary beds, it extends full two hundred miles further eastward. The exact outlines of 
the great area occupied by rocks of this age are not yet known, but from the observation of 
the Canadian geologists on the Assinaboin, Dr. Hayden on the Upper Missouri, Captains Stans- 
bury and Frémont on the Platte, of Drs. Roemer and Shumard in Texas, of myself on the 
Santa Fé road, &c., &c., it is apparent that they occupy a larger space within the territory of 
the United States than those of any other firmation, and at least 500,000 square miles of sur- 
. face. I am aware that Mr. Marcou has represented the greater part of the country lying 
between the Mississippi and the Rocky mountains as covered with Jurassic and Triassic rocks, 
and has so colored his map. In regard to the accuracy of this conclusion in other regions than 
those traversed by our party I will not venture to decide, but in reference to the geology of 
our route he is certainly far from right. He has divided the country between Las Vegas and 
the great bend of the Arkansas about equally between the two formations I have mentioned, 
while in fa¢t not a single outcrop of either exists on our route throughout all that interval, the 
entire distance (450 miles) being taken up by Cretaceous and Tertiary strata. 
On the Moro and about Fort Union the surface rocks are coarse friable sandstones of Lower 
Cretaceous age, apparently the equivalents of those of the Moqui villages, &c., but here tinged 
with red; a change already referred to, and which is more marked further east. 
Streams, sheets and buttes of trap are conspicuous features in the scenery, not only of this 
vicinity, but of all the prairie country adjacent tothe Raton mountains. These mountains seem 
to form a great volcanic focus, similar in many respects to those of San Francisco and San 
Mateo; many of the summits showing the peculiar outlines and colors of trappean rocks, and 
the long lines of trap mesas filling the horizon in that direction. Like those before described, 
the Raton volcanoes had innumerable subordinate vents scattered over all the adjacent region, 
from which the flow of lava was, in part, subsequent to the erosion of the beds of many of the 
present streams; for, as in instances before cited, the melted lava, obeying the laws that 
govern the flow of water, has followed the lines of drainage, and dispossessed some of these 
streams of their beds. 
On the banks of the Ocaté the Upper Cretaceous strata again make their appearance and 
form the hills between the valleys of that stream and the Red Fork of the Canadian. 
The banks of the latter, at the crossing and nearer the mouth of the Ocaté, afford the best 
view of the Upper Cretaceous series obtained on our route. The coarse, reddish-yellow sand- 
stones (Lower Cretaceous) form the trough in which it flows from the crossing and the walls of 
the cafion below. Upon this rests the series of shales and limestones which I have called 
Upper Cretaceous, forming precipitous bluffs near the stream and hills which rise toward the 
east to the height of 500 feet. The exposures of the strata composing the summits of these 
hills is less satisfactory than at their bases, but it was easy to perceive that no marked 
change occurs from top to bottom. 
