38 
GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
boniferous limestone and sandstone before reaching Camp 66. In the Resume, be is quite posi¬ 
tive on this subject, observing that the Trias is replaced by the Carboniferous limestone, which is 
succeeded by granite, gneiss, &c. Gneiss was seen from Camp No. 67, near the summit, both 
north and south of the camp. The width of this exposure of granitic rocks is about twelve 
miles along the route, and this is the distance given by Mr. Marcou in his Resume. The survey, 
however, crossed the range at one of its lowest points, where, also, the wide-spread sheets of 
lava had covered much of the rock from view. There is no doubt that a few miles either north 
or south the granitic rocks have a much wider exposure, as the mountains rise to a great height, 
and are composed of hard, rugged rocks. The chain, or the granitic exposure, does not, how¬ 
ever, extend many miles north, as Mr. Campbell crossed from the head-waters of the Rio San 
Jose to those of the Puerco of the west, several miles northwest of the summit, at Camp 67, 
without crossing the granite, he being on the red sandstone strata all the way. He saw the 
granite on the south of his trail, and also noted a bed of limestone, which is probably Carbon¬ 
iferous. This limestone is believed to be on the eastern flank of the mountain, and to dip 
towards the Rio Grande. It appears from Mr. Marcou’s notes that the summit-rock at the 
pass, at an elevation of 8,000 feet, is of limestone and sandstone, with the strata dipping west. 
He thought it most probable that these strata were Carboniferous, and so denominates them in 
the Resume. Lieutenant Whipjde, when describing the characters of the summit or dividing 
ridge between the ravines on opposite slopes of the mountains, says that the rock is a compact 
limestone. The presence of the red sandstone is also recorded by Mr. Marcou, and it contains 
its usual associate, the white gypsum. 
On descending from the summit the trail passes a lava stream which appears to have pro¬ 
ceeded from the south, where Mr. Marcou saw a high mountain, to all appearance a volcano 
with two or three secondary cones, the highest of which was estimated at 10,000 feet. This 
is the third volcanic centre noticed along the route. Mr. Campbell informs me that this stream 
of lava which was crossed extends for a long distance northward along the base of the Sierra 
Madre. Before taking leave of the eruptive rocks of this mountain range, it should be remarked 
that it is apparently the continuation of the ranges at the north called Sierra de Tunecha and 
Sierra Chusca, at the western base of which Fort Defiance is located. This place has already 
become known, at least by name, to mineralogists as a locality from which great quantities of 
beautiful garnets are obtained. They are probably collected in the beds of streams flowing 
from the granitic and metamorphic rocks of the mountains. 
Region ivest of the Sierra Madre. —The country west of the Sierra Madre presents, in its 
topographical aspect, a great similarity to that on the east of the Sandia and Santa Fe mount¬ 
ains, except that it is more cut by streams, and is not, on the whole, so arid and forbidding. It 
is a region of elevated table-lands of nearly horizontal strata, which are cut through in all 
directions by the streams, leaving here and there isolated mesas of all areas, from a few square 
feet to many square miles. Lieutenant Simpson, who was one of the earliest explorers of this 
region, describes the country as consisting of “ low mesas, blackened along their crests by out¬ 
crops of basalt.” At other places the white and red sandstone strata are moulded into fantastic 
shapes, “ some of them looking like steamboats, and others presenting very much the appear¬ 
ance of facades of heavy Egyptian architecture.” 1 The singular forms which these strata assume, 
by the erosion of streams and long exposure to the weather of that peculiar climate, have 
attracted the attention of every traveller, and resemblances to buildings and steamboats are con¬ 
stantly noted. The isolated columns, with the natural layers of the rock piled one on another 
with the utmost nicety and regularity, are often mistaken for works of art, and monuments of 
giant races now-lost to the earth and to history. 
El Moro , or Inscription Iiock. —This rock, already made famous by the number and variety of 
the ancient inscriptions and hieroglyphics which adorn its face, is directly on the line of the 
survey and about sixteen miles distant from the summit of the Sierra Madre. I present here 
1 Simpson’s Navajo Report, p. 118. 
