50 GEOLOGY 
On the eastern declivities of the mountains we find large surfaces strewed with concretionary 
and botryoidal masses of chalcedony, agate, and crystallized quartz of different colors, and 
frequently of great beauty. Cartloads of specimens, which would be highly prized by miner- 
alogists, might be collected there. These minerals have been formed in the crevices and 
cavities of a soft and very cellular amygdaloid, which has been much decomposed, and the 
silicious minerals now strew its surfaces. 
The eastern foot-hills of the Black mountains are generally composed of basaltic trap, which 
is frequently columnar, and they are remarkable for the prevalence of a peculiar form which 
they exhibit.. A number of them are crowned by castle-like summits of columnar trap, having 
perpendicular faces, from the base of which a glacis, perhaps of several hundred feet, slopes 
off uniformly on either side. 
Tertiary strata—Among these foot-hills are many masses of sandstone and tufaceous conglom- 
erate, probably of Tertiary age, and very similar to those which skirt the western base of the 
range. 
The sandstones, where unchanged, are yellow and soft, and have been eroded into striking 
imitative forms. In some localities these strata are much metamorphosed; the tufaceous con- 
glomerate containing great quantities of onyx in nodular masses, which have been infiltrated 
into its cavities. This rock, under these circumstances, presents almost precisely the appear- 
ance of that containing onyx, &c., and metamorphosed by the action of thermal springs on the 
banks of Warm Chuck river, Des Chutes basin, Oregon.* 
LONG VALLEY. 
This is an interval of nearly level land some fifteen miles wide, lying between the Black 
mountains and the next succeeding range on the east. It extends north nearly to the Colorado, 
and communicates with the Mojave valley at its southern extremity. It is parallel to and some- 
what resembles the Mojave valley, but is much higher, (2,000 feet,) and is now traversed by no 
permanent stream, though there is every indication that a river of some size once flowed through 
it. It is quite possible that all or a part of the Colorado once found its way southward through 
this channel. ; 
This plain forms the first step in the ascent to the table-lands; and is probably in part under- 
laid by the Tertiary sandstones and conglomerates which form the hills on its western margin 
where we descended from the Black mountains. 
CERBAT MOUNTAINS. 
Long valley is bordered on the east by hills of trap and coarse gray granite, which form the 
approaches to a range of mountains having a trend nearly parallel to that of the Black moun- 
tains, but rising much higher, at the time of our visit (March 26) its summits being covered 
with snow. The highest portion of this range—a huge granitic mass, southeast of Camp 62—is 
visible from a long distance, and is a prominent landmark in all this region. At this point the 
range, apparently homogeneous southward, increases in breadth and altitude, then falls off to 
the north and divides into two distinct ranges, our route crossing above the bifurcation. 
The western range is principally composed of trap, trachyte, and porphyry, but all having @ 
very different aspect from those of the Black mountains. 
With the masses of these rocks, which are the immediate product of fusion, occurs a series 
of stratified tufas and conglomerates which have been buried beneath floods of molten matter, 
and to which they are in some places so closely assimilated by metamorphosis as to be with 
difficulty identified. , 
These beds are apparently composed of volcanic materials, principally ashes, stratified by 
© Pacific Railroad Report, Vol. VI, Part 2, page 49. 
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