Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

QUARTZ VEINS-IRON ORE-BEAR CREEK.
masses being five or six feet in diameter. The ore breaks with a smooth conchoidal fracture,
it being singularly compact and hard. It occurs interleaved with the slate, portions of the
rock being found in the ore.
This bed of iron oxide appeared to be the result of the decomposition of pyrites; and if so,
the undecomposed pyrites would be reached by sinking to a sufficient depth in the vein. It is
probably auriferous, but no gold can be seen in the oxide of iron or quartz. It may, however,
exist in quantity sufficient to pay for working. This vein conforms in trend and dip with the
slates, which resemble those in the gold region of North Carolina and Virginia.
Burns' creek.-A remnant of the former elevated plain of sandstone formed a picturesque
object near our route, and was sketched by Mr. Koppel.
It consists of a nearly circular disk of compact sandstone, ten or fifteen feet thick, capping
the summit of a round mound. Hills of this character, of greater extent and elevation, are
numerous for several miles south of this point.
Bear creek.-At Bear creek, twelve miles north of the Mariposa river, a good natural section
or vertical exposure of the strata composing one of these fiat-topped hills was presented. It
consisted of a series of beds of coarse and fine sandstone and strata of gravel and conglomerate,
which are represented in section, Chapter XIII., The whole elevation of the hill was estimated
to be about 150 feet. The following is the succession of the strata as observed from the top
downwards to the level of the creek. The thicknesses are given as they were estimated, and
are, therefore, merely approximate. The letters refer to the section.
SECTION OF THE STRATA AT BEAR CREEK.
k. Conglomerate.. —-----------------------------------------------------------.
j. Sandstone —--------------------------- ----------------------------------
i. Conglomerate —----------------------------------------------------------
h. Sandstone, fine.. —----------------------------------------------------------.
g. Conglomerate of gravel, white and black quartz, and nodules of carbonate of lime f
f. Sandstone, showing diagonal stratification and one or two layers of gravel —--------
e. Sandstone, with a layer of pebbles.. —------------------------------------------
d. Hard sandstone, thinly bedded; layer of pebbles towards the base —---------------
c. Compact sandstone, with some small pebbles —---------------------------------
b. Sandstone, with coarse grains and pebbles —---------------------------- --------.
a. Sandstone ----------- -
.The upper stratum is perfectly level on the top and free from soil; a dwarfed bush or tree,
here and there, is the only vegetation. The whole surface appears fissured, or as if cracked by
drying in the sun-precisely as the soil is cracked during the dry season. This iust have
taken place at the time of the deposition of the rock or soon after. On closely inspecting the
slight accumulations of fine gravel in some of the hollows of the rocks, numerous very slall
but beautiful crystals of andalusite were found. These did not exceed three-sixteenths of ar
inch in diameter, and were seldom over one-eighth. They are translucent, but appear to be
worn and rounded by attrition.
From the summit a fine prospect was preseuted towards the south. The broad valley of the
San Joaquin was in full view, and it was dotted by numerous isolated flat-topped hills, standing
like islands in the plain. Bear creek was entirely dry at the point we crossed; higher up the
stream, in the hills, large quantities of gold have been obtained, and the stream is noted for the
number and magnitude of the nuggets it has produced. The gold is not evenly distributed; it
is found only at intervals, as might be expected from the size and weight of the masses. For
this reason the diggings are called spotted by the miners.
15
6 feet.
50 "
22 "
1 foot.
10 feet.
12 "
3 "
20 "
2 "
1 foot.