CARBONIFEROUS FOSSILS—GRANITE—AZTEC MOUNTAINS. 4T 
rises about forty miles southwest of San Francisco mountain, and, like it, has poured out im- 
mense fields of lava which cover nearly the whole region. The first stream from this crater 
was crossed at the head-waters of Parke creek, just beyond Camp No. 95, but the most extensive 
overflow was not found until the survey reached the head-waters of Partridge creek, at Camp 
97, the lava being continous from this point to the Picacho, or Camp 99, a distance of twenty 
miles. The greatest flow from this mountain appears to have been towards the north or north- 
west. The lava extends north of the trail, and spreads out at the base of an eminence called 
Pineveta, which is probably of stratified rocks. 
Carboniferous limestone.—The occurrence of limestone containing carboniferous fossils, near 
Camp No. 95, has already been mentioned. Mr. Marcou found at this locality three or four beds 
filled with fossils like those at the Pecos villages. He enumerates them in his notes as Pro- 
ductus reticulatus, P. punctatus, Spirifer, Terebratula, and Polypi. These were very abundant 
and formed a lumachel. Some fossils from this locality are in the collection, but they are so 
badly preserved, that their specific characters cannot be determined. It is doubtless the carbon- 
iferous limestone. It would appear that this limestone extended for several miles along the 
trail, and was found beyond Camp 96. It will be seen, on looking at the map, that the lime- 
stone called magnesian, along Parke creek, is in close proximity with these outcrops. 
After leaving the carboniferous limestone beyond Camp 96, the trail passed over a bed of lava, 
and then Mr. Marcou found sandstone strata dipping from sixty to eighty degrees, and trending 
northwesterly. He considered this sandstone to belong to the upper Carboniferous formation. 
He describes the strata as hard and schistose, harder than the ** New Red’’ sandstone of the 
prairies. Beyond the sandstone, lava was found, it being the eastern edge of the broad overflow 
proceeding from Bill Williams’ mountain, on the south. This lava covers all the subjacent rocks 
for twenty miles, except in the ravine of Partridge creek, which cuts through the lava and ex- 
poses in many places a greyish-white limestone, probably carboniferous. At Camp 99, which is 
on the western border of the field of lava, carboniferous sandstone is again found, with beds 
dipping north. 
Granite. — À mountain called Picacho was visible a few miles north of Camp 99. This was 
thought to be granitic by Mr. Marcou ; it was also the opinion of Mr. Campbell. The outline of 
the view on page 85 of Captain Whipple's report, tends to confirm it. One mile southwest of 
Camp 99, or at Camp 100, outcrops of granite and gneiss were found. This rock trends north- 
west and southeast, and forms the bottom of the Val de China. This granite was covered by 
the beds of carboniferous sandstone. Limestone was not noted. I find two specimens of granite 
in the collection from the Camp near Picacho, Nos. 23 and 36 of the catalogue. The granite is 
rose-colored, and one specimen contains a light silvery mica in distinct plates; the other has a 
much finer grain, and is so granular as to resemble sandstone. Two other specimens are from 
this locality—Nos. 52 and 53—labelled basalt and obsidian. They appear to be transported 
fragments. 
Carboniferous limestone.—Seventeen miles southwest of this outcrop of granite, Mr. Marcou 
notes a table-land formed of carboniferous limestone, at the foot of which the party encamped. 
The trail continued at the base of this cliff for nine miles. Mr. Marcou mentions seeing crinoids 
and some species of Productus in the creek. He also mentions an outcrop of carboniferous 
sandstone before reaching Camp 102. 
Aztec Mountains.—We have now reached a portion of the line where the geology Lidil ex- 
ceedingly interesting. Since Camp 99, the course of the survey deflected south in order to turn 
a southern point of the Aztec mountains. These mountains trend northwest and southeast, 
and have a flat, table-like summit, composed of stratified rocks dipping gently to the east or 
northeast, These strata present a bold precipitous front towards the southwest, forming i in one 
place the summit of a cliff 1,200 feet high. This cliff, according to Mr. Marcou, in his notes, 
January 22, is composed of granite from the base to the middle ; on this rests a bed of sandstone, 
then ae and grey sandstone on the top. The solicito the strata to the underlyii 
