10 LIMIT OF THE LLANO ON THE EAST.—ESCARPMENTS OF ROCK. 
been attributed to it. "The descent from its summit to the headwaters of the Colorado was so 
gentle as only to be perceptible to instrumental survey; and there was nothing to mark its eastern 
limit, except the existence of the tributaries of that stream. Neither bluff nor uncommon swell 
of the ground marks its existence as you approach from the east or west, nor is its uniformity 
of surface disturbed at any point between the Pecos and the Colorado.’’! These observations 
are exceedingly interesting, and of importance to the question of the location of a railroad. It 
is possible, however, that this gentle inclination or descent from the surface of the Llano, both 
on the east and west, is local, and caused by peculiar erosions or degradation of the plain at those 
points. The Colorado river, at the eastern border of the plain, has numerous affluents; and it is 
to their continued wearing action that we may look for the destruction of the abrupt precipices 
which mark the Llano at other places. The regular swell of the Llano, as exhibited on Capt. 
Pope's profile, may thus result entirely from extensive lateral erosions along that portion of 
the Pecos, and not be due to the presence of a subterranean ridge of older rocks, as has been 
suggested. 
According to the profile which Captain Pope has presented, the elevated plain of the Llano 
may be considered to extend from the Guadalupe mountains, or the Pecos, to a point beyond the 
Colorado, or the divide between it and the Brazos river. This point is 4,236 feet in altitude, and 
from it the surface descends very regularly for nearly 275 miles, to the banks of Red river, at 
the termination of the line of survey, only 641 feet above the tide-level. 
In the descriptions by Captain Pope, however, he regards the sources of the Colorado, or the 
Sulphur springs, as the eastern limit of the Llano; and the character of the country indicates a 
change in the nature of the rocks and soil. I have, therefore, concluded that the geological for- 
mation composing the surface of the Llano does not extend on the line of the trail to the east 
of the Sulphur springs, and I have so represented it upon the geological map. 
Rivers and streams.—The principal streams which traverse or take their rise in the Llano, 
are the Canadian and Red rivers, the Brazos and Colorado, and the Pecos. The first named 
flows from its sources in the mountains near Santa Fé, almost directly east, and intersects 
the Llano; the Pecos, also rising in the same place, flows not across the plain, but southerly, 
parallel with the mountain ranges, forming a long valley of erosion. The other rivers ap- 
pear to rise near the eastern margin of the plain, and are formed by the union of nume- 
rous minor afluents, after they emerge from the canons of the plateau. With very few 
exceptions, wherever these streams traverse or intersect the Llano, they are characterized 
by bold, bluff banks or walls, on either side, which are almost impassable, and confine the 
traveller to the tortuous course of the stream ; while, above, the level surface of the plain stretches 
out and affords a boundless prospect in every direction. The vertical banks near the sources of 
Red river are graphically described by Captain Marcy in his report, as follows: ‘‘ The gigantic 
escarpments of sandstone, rising to the giddy height of 800 feet on each side, gradually closed 
in until they were only a few yards apart, and finally united overhead, leaving a long, narrow 
corridor, ioo si the base of which the head spring of the principal branch of Red river takes 
its mee 7 * “The stupendous escarpments of solid rock rising precipitously from 
the bed of the river to such a height as for a great portion of the day to exclude the rays of the 
sun, were worn away by the lapse of time, and the action of the water and the weather, into the 
most fantastic forms, that required but little effort of the imagination to convert. into works of 
art, and all go in forming one of the grandest and most picturesque scenes that can be im- 
sphiat " * * “Occasionally might be seen a good representation of the towering 
walls of a duds of on feudal ages, with its giddy battlements pierced with loop-holes, and its 
projecting watch-towers standing out in bold relief upon the azure ground of the pure and trans- 
parent sky above. In other places, our fancy would metamorphose the escarpments into a bas- 
tion front, as perfectly modelled and constructed as if it had been a production of the genius of 
a Vauban, with redoubts and salient angles all arranged in due order.''? 
* Report of Captain Pope, p. 9. * Exploration of the Red river by Captain Marcy. [33d Cong., lst sess., pp. 55, 56.] 
