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.
is not less than three feet, and it is so abundant as to line the whole bed of the stream, hiding-all
the rocks from view. Portions of the mass were traversed with long cylindrical tubes; they
being the casts of reeds and rushes similar to those now growing in the water. This stream
runs towards the valley of the Ancient Lake, and at certain seasons of tke year may deliver a
large quantity of water. It serves as an indication of the source of the calcareous water of the
former lake, and there are doubtless many other streams of a similar character in that vicinity.
It is singular that the name of this valley is already associated with calcareous springs in
Europe. The springs and baths of San Fillipo, in Italy, are famous for the quantity of lime
contained in the waters and for the manufacture of medallions by its deposition. The water
which supplies the baths falls into a pond, where it has been known to deposit a solid mass thirty
feet thick in about twenty years.1 It is also stated that "a hard stratum of stone, about a foot
in thickness, is obtained from the waters of San Fillipo in four months; and as the springs are
powerful, and almost uniform in the quantity given out, we are at no loss to comprehend the
magnitude of the mass which descends the hill, which is a mile and a quarter in length and the
third of a mile in breadth, in some places attaining a thickness of 250 feet at least." "A large
proportion of the most splendid edifices of ancient and modern Rome are built of travertin,
derived from the quarries of Ponte Lucano, where there has evidently been a lakge at a remote
period.' 2
The calcareous deposits on the shores of the Ancient Lake are not crystalline or stalactitic,
nor do they exhibit distinct layers or successive coats, as is the case where the deposition
proceeds under full exposure to the air, and the water flows over the surface slowly, or in a thin
layer. On the contrary, the deposition appears to have been rapid, and below the surface of
quiet water.
The sinter of Pilot Knob is less compact than that marking the shore of the lake, and does
not appear on the surface of the rocks, being confined entirely to the clefts and crevices, as if it
had originated there instead of being deposited from without. This was very possibly the case.
The fissures may have given passage to the calcareous water from below. The specimen which
was collected has been analyzed for me by Dr. J. D. Easter with the following result:
Insoluble residue (silica) ----------------------------------— 8. 629
Carbonate of lime ---------------------------------- 85.70
Sulphate of lime -----------------------------------------— 0.246
Carbonate of magnesia ------------------------------------— 0.449
Peroxide of iron. ------------------------------------------- 1.11
Alumina. —----------------------------------------------- 2. 085
Silicate of soda. -------------------------------------------- 0. 847
Chloride of sodium ----------------------------------------- 0.346
Phosphoric acid -------------------------------------------- trace.
99.412
Further observations on it will be found in the Appendix, Article VII, Specimen 250.
THE SAND-HILLS.
The sand of the Colorado Desert forms, as has been shown, but a small part of its surface.
It is not found in a broad and thin layer, but is gathered together by the wind into heaps and
drifts, serving to break the monotony of the level'plain. These hills are remarkable for the
1 Dr. Grosse on the Baths of San Fillipo. Ed. Phil. Journal, ii, p. 292.
2 Sir Charles Lycll, Principles of Geology, p. 242-243.
240