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

GEOLOGY.
margin of a table land or gentle slope, that inclines slightly towards the south, and becomes
merged in the slope of the Tulare valley. It is a portion of the former plateau of Tertiary
strata, but is much lower than the other portions undoubtedly were, and it may, therefore, be
concluded that the former sedimentary plain sloped gradually off in this direction, thinning down
to the level of the Tulares.
A view of this long even bank is given in the sketch. The round Tertiary hills are seen in
the foreground, and Posuncula river, with its broad delta, occupies the centre of the scene. The
broad belt of timber is on the sloughs of the river bottom, where it spreads out near the southern
lakes of the Tulares. The western border of this belt of Tertiary formation, from Pose creek
southward to Posuncula river, slopes off to the west, and passes insensibly into the Tulare plains
by a succession of gradual and gentle undulations of the surface.
It appears that the sand and gravel that has been brought down from these Tertiary hills by
alluvial action has been deposited along at their base; while the clays and finer volcanic sands
have been carried further out into the Tulares. In this way a narrow margin of nearly level
surface, composed of gravel and sand, has been formed at the base of the sedimentary hills,
separating them from the soft and clayey soil of the Tulares. This narrow belt affords a good
foundation for the construction of a railroad.
Posuncula, or Kern River, to the Tejon Pass, September 2-31.13 mile8.-The hills and remnants
of the elevated plateau adjoining Posuncula river exhibit, in many places, accumulations ofcobblestones and small boulders much above the present level of the stream. They are, doubtless, the
remains of the drift of a former bed of the river, when it flowed at a higher level than now, as
they do not appear to have been derived from the subjacent strata;
Posuncula river, at the ford, is a deep, rapidly flowing stream; and its banks are lined with
great accumulations of drift rocks, in masses much rounded by transportation in water. These
consisted principally of syenites and basaltic and flinty rocks, varying in size from six inches to
two feet in diameter.
Fossil stem3. -Among these boulders I found a mass of a jaspery, silicious rock, of a yellowish
color, that was filled with silicified fossil stems, preserved so completely that every cell and
tube was distinctly visible. Some of the fragments are represented of the natural size in the
annexed figures. The oblique section of the stem was drawn so as to show the arrangement of
the cells and radiating lines.
FOSSIL STEMS OF PLANTS.
The boulder containing these beautiful stems was about eighteen inches in diameter, and is
a short distance below the ford, on the right bank of the stream. It must have been transported from the headwaters of the river, or from the sedimentary beds a short distance above,
having been broken out by the action of floods. It is very desirable that the original locality of
these fossils should be discovered, and their geological associations made known. It is probable
that the examination of the rock in situ would develop many interesting forms n6t found in
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