CRETACEOUS—LAY A-SIERRA MADRE. 
37 
continuous between Camps 63 and 64, and, indeed, was subsequently found along the valleys of 
all the streams as far west as the volcano of San Francisco. This formation appears to differ 
from that under the white or light-colored sandstones on the east side of the mountains, by 
the absence of the thick beds of red clay or marl. Here, the summit is formed of red argil¬ 
laceous sandstones. Under this, gypsum occurs, and then red sandstone again. (See notes, 
November 13.) On the banks of the San Jose, just below Lagunas, the black front of a stream 
of lava is found, which appears to have followed the river valley. This, according to Mr. Mar- 
cou’s observations, is one of the streams of an extinct volcano called San Mateo, and by Lieu¬ 
tenant Simpson, Mount Taylor. It rises about twenty miles north of the line of survey, and 
has covered the surrounding country with its outpourings of molten rock, which now rests like 
a black mantle over the horizontal sedimentary strata, and in many places protects them from 
denudation. According to Lieutenant Simpson, this peak can be seen from Fort Marcy and 
other places over one hundred miles distant. 
Beyond Laguna, the sides of the valley were formed of blue clays, covered by yellowish-grey 
sandstone ; these are surmounted by strata of yellowish-blue clay, containing fossils. In the 
notes, Mr. Marcou calls these fossils Gryphcea dilatata, and scales of saurians. Higher up, a 
yellowish-grey sandstone is found, containing “ Area and Irsocardia.” The lava proceeding 
from the volcano, Mount Taylor, covers all these strata. (See notes, November 14.) The 
occurrence of these fossils at this locality, so near the bed of coal, is very interesting and im¬ 
portant, but no specimens are found in the collection. 
Beyond Covero, the light-colored sandstone is exposed for a short distance, and is then hid 
from sight by a covering of black lava. At a point five miles from the village, the trail passed 
a stream of scoriae, which was found to be continuous to Camp 65, where it was in connexion 
with the lavas which come from San Mateo. “ The lava and scoriae are black and porous, with 
all the conditions of plications and contortions which are found in other countries.” (See Mr. 
Marcou’s notes, November 15.) Lieutenant Whipple observes as follows : “ The whole length 
of the valley followed to-day has been threaded by a sinuous stream of lava. It appears as if it 
had rolled down a viscous semi-fluid mass, had been arrested in its course, hardened, blackened, 
cracked, and in places broken, so as to allow the little brook to gush out from below, and gurgle 
along by its side. The lava bed is frequently a hundred yards in width, the cross section being 
a semi-ellipse, in the centre probably thirty feet high.” 1 This peculiar undulating and curved 
surface, so characteristic of lava streams when partially cooled, was also noticed by Lieutenant 
Simpson just before entering the valley of San Jose. At that point there were “ hundreds of 
acres of volcanic rock, a great deal of it exhibiting with marked distinctness the undulations of 
the wave, in its oscillatory motion.” 2 
Between Camps 65 and 66, Mr. Marcou records a great lava stream called the Coulee ; this is 
two or three miles wide, and extends to, and beyond, Camp 66. About twenty miles northwest 
of Camp 65, and on the borders of the San Jose, there is a crater from which a very considerable 
stream of lava has descended, and flowed southeast along the valley. It is believed to be con¬ 
tinuous to near Camp 65, and to mingle with the streams which have descended Mount Taylor. 
The position of this crater is shown on the map. 3 
Sierra Madre■—Granite and carboniferous rocks. —Camp No. 66 was upon the granitic rocks 
of the Sierra Madre, the second great mountain range crossed by the survey. This granite, 
according to Mr. Marcou, is coarse-grained, and of a rosy color. There is but one specimen in 
the collection, No. 6 of the catalogue and description. It is coarse-grained and feldspathic, 
containing two varieties of this mineral, one white and the other red. A white, silvery mica is 
also present. This granite appears to have been exposed from Camp No. 66 to No. 67, where it 
was covered by lava. Mr. Marcou mentions the possibility of his having passed outcrops of car- 
1 Lieutenant Whipple’s Report, p. G2. 
3 Simpson’s Navajo Report, p. 128. 
3 1 am indebted to Mr. Campbell for this information. 
