174 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
strata of the Coast mountains beyond. These formations are nearly parallel with the lines of 
uplift along the Mojave, and should be represented on the same section with them, if it were 
intended to show fully the geological structure from the Pacific to the Mississippi, along the 
35th parallel. As, however, the line of survey did not extend across the Great Basin and reach 
the Sierra Nevada, and as the geology of that portion of the country is considered in my report 
on the geology of the routes surveyed in California by Lieutenant R. S. Williamson, Topo- 
graphical Engineers, I do not extend the section in that direction, but follow the line of the 
survey, which, although deflected to the south, intersects the mountains at nearly right-angles 
with their cy 
The portion of the section which conforms least to the line of the survey is between the Colo- 
rado and the Big Sandy rivers, or from Camp 133 to Camp 110, in Cactus Pass. Here the line 
of section is direct, and transverse to the trends of the ranges, and avoids the long curve to the 
south through the valley of the Colorado and the Hawilhamook or Bill Williams’ fork. 
The next point of divergence of the line of section is at Camp 106, where it extends ina 
straight line to Camp 97, and permits the horizontal position of the carboniferous strata to be 
conspicuously shown. In order to permit the full breadth of the Llano Estacado to be repre- 
sented, I have carried the line eastward from the Sandia mountains over its surface, intersecting, 
however, the ravines which isolate Tucumcari hill from the plateau. If the section followed 
the trailin the valley of the Canadian, the full width of the Llano would not be represented by 
many miles, unless it was sketched in beyond the trail. The line of section being thus broken, 
is resumed again at Camp 42, nearly north of the eastern bluff of the Llano. `; 
From the Antelope Hills to the eastern base of Delaware ridge the line is diis bat yet 
coincides very nearly with the trail, from which it is not far removed at any point. The direc- 
tion of this part of the section is nearly southeast, and it thus makes a favorable section of 
Delaware ridge, which trends northeasterly. Itis believed that if the section were continued 
in this direction to the Gulf of Mexico, it would present the best view of the geological structure 
of the line, for at this point the formations trend northeasterly, and are traversed by the survey 
in a nearly parallel line. Ifthe section continued southeast beyond Delaware ridge, the out- 
crops of the granite along Boggy creek would be intersected, and the succession of Carboniferous, 
Cretaceous, and Tertiary formations would appear beyond. The granite of Boggy creek may 
be regarded as a portion of the same line of uplift which appears at the Hot Springs of Arkansas 
and at Little Rock. It was deemed best, however, to confine the section as much as possible to 
the line of survey, and thus a great breadth of carboniferous strata is represented between 
Delaware ridge and Little Rock—a much greater breadth than would appear if the line of sec- ` 
tion were transverse to the trend. The fact that these ridges of sandstone are for the greater 
part of the distance parallel with the section should be remembered when it is examined, 
In general, where the line of section coincides with the trail, the formations, as they appear | 
along the trail, are shown; but in some cases important or interesting features which occur 
within a short distance Eë north or south, are represented as if they were intersected by the 
trail. Where the line of section does not coincide with the trail, but diverges from it, the 
formations which it intersects are represented if they are known or can be correctly inferred; 
but in some cases outcrops of strata found along the trail are referred to the line and represented 
as if intersected by it. Examples may be found in the representation of Rock Mary, which 
rises north of the section-line, and in the natural mounds near Camp 37, and the cretaceous 
deposites near Camp 39. Sugar-Loaf mountain, although only thirty miles south of Fort Smith, 
is sketched in upon the section near Dardanelle rock, it being regarded as forming a portion of 
that line of elevation. This mountain might, however, be very properly represented near Fort 
Smith, as that portion of the section is nearly parallel with the strata, and does not purport to 
be a representation of the structure of the region. 
The several volcanoes are sketched in above the other formations, and are not represented in 
section, as neither of them were ascended and the forms of their craters ascertained. . 
EL 
