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

METAMORPHIC ROCKS-TERTIARY STRATA.
in the specimens, but in some, garnets and magnetite were abundant. The size of some of the
masses of ore, and the number of the fragments of this peculiar rock, indicated the existence of
very considerable quantities up the valley, and we may expect to discover a valuable bed of
iron ore in that region.
GRAPHIC SYENITE, WILLIAMSON'S PASS.
The lower part of the pass is narrow, and bounded on each side by ridges of white granite,
the sandstone being beyond. About sixteen miles from the summit, the granite hills become
higher, and the stream winds in a circuitous course around projecting points of the ridges. Here
the granites no longer have the peculiar whiteness, but are highly laminated and micaceous,
becoming gneissose, and have the usual dark color. The planes of lamination are bent and contorted, and veins of feldspar and quartz traverse the rock in various directions. These rocks
are in all probability metamorphic, and in appearance they present a great contrast to the
white and chalk-like granite which forms the hills along a great part of the pass.
Low, rolling hills.-About 19 miles from the summit the granitic hills disappear, and the
valley is bounded by low hills of sandstone and conglomerate. The country opens, and a view
is presented for long distances in various directions. The strata are exposed all alongthe
stream, and dip, at small angles, in different directions; but as we proceeded further from the
igneous rocks of the pass, the flexures became more and more gentle, until the strata were
nearly horizontal. It will be seen on the map that this part of the pass is not far from the
point where sandstone strata were examined in the lower part of the Pass of San Francisquito.
They are evidently the same series of sediments, and they form the bounding hills of the valley
of the San Francisquito Rancho. The low hills, however, at the borders of the granitic ridges,
have a more recent appearance than the uplifted strata higher up in the valley, and they may
differ greatly in age. The coincidence of the direction of the pass and of the other principal
valleys with the trend of the rocks is worthy of notice, and is well shown on the map. The Pass
of San Francisquito, in its upper portion, is an exception to this observation, the valley of the
creek being nearly transverse to the trend of the granite it crosses; it is, however, a narrow,
rugged caon in that portion of its course, and it does not compare in extent with the long, low
valleys occupied by the sandstones.
We met with considerable difficulty in portions of the pass from the growth of timber and
willows along the creek, which filled the whole valley between the ridges on either side and
prevented us from progressing, so that we were obliged to cut our way through the thickets and
form a road for the wagon; with our small number this was a serious undertaking and occupied
much time. On the 26th we cut a road one-fourth of a mile long through the timber, and was
obliged to cut again on the 27th and 28th; as we had but one axe, sheath-knives and heavy
clubs were brought into use, with which the brush and vines were levelled to the ground. An
old pack-trail was found along the sides of the ridges, and was probably formed when the copper
locality was prospected.
San Francisquito Banc/to, October 28.-After we emerged from the ca-non in the granites, and
71