26 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
sandstones, as on Rocky Delaware creek. It also appears that the light-colored sandstones and 
calcareous beds constitute the main part of the bluffs, and that the red marls and clay of the 
gypseous series are at their base and occupy the space between them and the river. 
The trail then, after passing the Antelope hills, passed for a time over grey sandstones and 
their débris, then upon the red clays and sand for several miles, until at Camp 43, on Arroyo 
Bonito, grey or white sandstones were again found on the banks of the creeks. Beyond this a 
succession of variegated marls was seen, but gypsum was not found 
At Camp No. 45, on Amari creek, the ascent of the bluffs of the Llano was commenced, and 
its surface was traversed for a few miles, and then the survey again traversed the red clays of 
the gypsiferous formation in the valley of the Canadian and its tributaries, until the mounds 
just described were reached. 
Plaza Larga.—This place, so called by the Mexicans on account of the wide and fertile vallas 
of the Rio Tucumcari, is at the base of the Tucumcari hills, and about two hundred miles east of 
the Rio del Norte. Its soil probably consists of the red clays and sand, mingled with the debris 
of the strata of the Llano ; and, according to Mr. Marcou, it is without alluvium, not even of 
fragments of sandstone or limestone. "The border bluffs of the Llano here recede to the south, 
and Tucumcari hill stands in the centre of the curve. They again extend to the north, and over- 
hang the route beyond Plaza Larga, and near Laguna Colorado, at Camp 50. The road also 
between Camps 50 and 51 is near the bluffs, but is on the red clay formation. At Camp 51 the 
wide valley of the Pecos and Hurrah creek is reached, and the bluffs of the Llano again bend 
southward and disappear. This part of the route is among isolated hills, which are remnants 
of the once continuous Llano, and now stand as monuments of its destruction, but agree with 
it in their geological structure. 
REMNANT OF A STRATUM OF SANDSTONE NEAR LAGUNA COLORADO. 
One of the projecting bluffs passed by the expedition was surmounted by a singular outlier 
of the rock, poised upon a narrow base. It is an interesting example of weathering and decay, 
