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

STRUCTURE OF THE METAMORPHIC ROCKS.
acter of the rocks could be made evident. The representation is thus confined between the line
of profile and one drawn parallel with it, and a short distance above. This line is entirely
arbitrary, and is used merely to limit the extent of the signs used to denote the character of the
rocks. The elevation and general character of the outline of the ridges and summits is shown
by the lines sketched in above the line of profile.
SECTION OF THE SIERRA NEVADA AT THE TEJON PASS.
- Granitic and metamorphic rocks.-The rocks now generally classed as metamorphic by geologists, and known as gneiss, mica slate, hornblende slate, and chlorite slate, are the predominating formations of the Sierra Nevada at the Tejon. They present various appearances,
corresponding very nearly with those of rocks of the same name on the Atlantic slope of the
continent; but they vary so greatly in their apparent composition, and in the relative quantities
of the composing minerals, and they pass by such insensible gradations from one to the other,
that no well-defined line of demarcation can be found between them. The transition from these
rocks to compact granite and syenite is also gradual, and even these last named rocks present
traces of lamination, or structure, which closely connect them with the others.
In the following descriptions of these rocks, the use of terms, or names, indicating the
existence of separate formations, will therefore be avoided as much as possible, and, in general,
the rocks will be described by specifying the predominant minerals and their state of aggrega
tion. This absence of well-defined lines of separation between the different varieties of the
rocks also prevents a representation of them by different colors on the map and sections. The
attempt has, however, been made to indicate the variations in the rock, and the extent of laination, by means of fine lines. These representations are accompanied by short notes on the
lithological characters. In some cases where the names mica slate, hornblende slate, chlorite slate,
&C., are appropriate, and will not lead to a misapprehension of the true structure of the rocks,
they are retained. The rocks will be described in their order of succession from west to eastfrom the most western outcrop at the margin of the Tulare plains to the last exposure at the
slope of the Great Basin on the east.
The following detailed description of the granitic rocks of the most western ridge will serve
to give an idea of the general structure of the rocks in the main part of the chain, and to explain terms which will frequently be used in succeeding descriptions:
Although the rocks of this ridge may be called granite, or granitic, they are not compact
and homogeneous, but consist in great part bf hornblende, feldspar, and mica, arranged in long
parallel lines, so as to give a slaty character to the mass. The hornblende and feldspar are
found in long belts and in lenticular masses intercalated with mica, veins of feldspar, and
seams of quartz. These lines, or belts of different mineral composition, are exceedingly
numerous, and present frequent alternations with each other. There is not, however, any
well-defined line of separation between them; the transition from one to the other being
gradual, and almost imperceptible. Where the mica predominates, the surface decomposition
appears to have been the most rapid, and the portions of rock containing the harder minerals
are left standing in relief. A portion of the rock has a compact syenitic character, and, in
addition to the minerals already mentioned, contains lines of epidote and garnets. Many lines
of these minerals are often found in the width of a single inch; they extend for long distances
in nearly parallel lines, and often have a local divergence or bulging, surrounding lenticular
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