14 ROCKS WITH HIGHLY POLISHED SURFACES.—GUADALUPE MOUNTAINS. 
vicinity of Los Cornudos, (Thorne’s wells.) It is a peculiar porphyritic rock, of a light-grey color, 
with a faint shade of lilac. It is evidently eruptive, and may be called trachyte, the feldspar 
being in glassy crystals, and apparently imbedded in a less crystalline base of the same mineral. 
Hornblende is present in small black crystals, and a small hexagonal plate of dark-red mica is 
also visible. It is entirely different from the granite found at the Hueco mountains, and its 
characters are more nearly like those of recent erupted rocks, such as occur in dykes, and not 
in broad, extensive masses. 
Mr. Bartlett noticed a peculiarly polished surface on all the rocks of that UE ; in one 
place, it was so distinct that it appeared ‘‘to have been done by the hand of man.’ 130.) 
This phenomenon was again presented near the Hueco tanks, where are some isolated granite 
precipices standing alone in the plain; the surface was so highly polished, that Mr. Bartlett 
remarked it particularly, and says that they were as smooth ‘‘as if they had been submitted to 
some artificial process. It was probably the effect of their exposure for ages to the weather.''! 
I have very little doubt that this peculiar polished condition of the surface is precisely like that 
of the rocks on and around the Colorado desert of California. "There, the rocks, as I have shown 
in a recent report,? receive their smoothness and high polish by the long-continued action of the 
grains of sand and of dust which are carried over their surfaces with velocity and force by the 
winds. This is probably the cause of the polished surface of the rocks of the mountains under 
consideration. On the desert, the climate is such that there is little or no perceptible disinte- 
gration of the rock, even after ages of exposure. This is peculiarly favorable to the production 
of the polished surface; for the cause is continually acting, and there are no opposing influences. 
Guadalupe mountains.—' The specimens from the Guadalupe mountains are all of limestone 
and sandstone, and I do not find any of the erupted rocks represented. From the general 
topographical indications, I am led to regard this range as having a granitic axis, or as being 
on the crest of an uplift of granite and the allied rocks, although they may not appear upon 
the surface. The specimens (particularly Nos. 5 and 6, see catalogue and description,) are, 
however, of stratified rocks; and in the absence of any evidence of the presence of the Plutonic 
rocks, I have not represented them upon the map or section at the point crossed by the trail. 
The peculiar divergence of the mountains towards the northeast, and their apparent prolonga- 
tion in the Witchita mountains, which has already been noticed, and the connexion of the range 
on the south with a range known to be granitic, together with its great elevation and rugged 
character, lead me to consider it highly probable that granite will ultimately be found in some 
parts of the range, north or south of the part explored. Although there are no fossils in the 
specimens of limestone from the Guadalupe, and thus there is no evidence of the age of the 
rocks, I cannot but regard them as Carboniferous, and I nave colored the range near the trail 
accordingly. 
This opinion is strengthened by the following description, by Col. A. B. Gray, of the Guada- 
lupe peak, which rises on the north side of the Pass: ‘‘There is an abrupt and precipitous cliff 
of columnar rock upon vast limestone terraces, attaining a height of 1,000 to 1,500 feet above 
its base, with a general elevation of several thousand feet above the plain. It can be seen ata 
great distance, owing to the clear and rarified atmosphere of the country. The face of this 
stupendous structure is perpendicular, and looks as if it had been shaped by some sudden and 
powerful convulsion of nature into the form of a large edifice or church, from which we gave it 
the name of Cathedral rock. Viewed from the deep gorge below, it is truly sublime and beauti- 
ful; its lofty peak towering to so great an altitude, and crowning the terminal point of an exten- 
sive range of mountains." * Messrs. Bartlett and Marcy give similar descriptions of this 
locality, and there is little or no doubt of the stratified character of the mountains. 
! Bartlett, p. 175. 
? Preliminary Geological Report in connexion with the report of Lieut. R. S. Williamson. See also the final report. 
? For a description of these specimens, see a subsequent portion of this repo: 
* Report of A. B. Gray. [Railroad Record: Cin., October, 1855, vol. iii, hot No. 136, p. 13.] 
