12 GEOLOGY. 
melons were abundant. At this point on the river there were evidences of three distinct 
terraces, rising one above the other at heights of about fifty feet each. The upper one is much 
cut and furrowed by rains, and now forms a succession of low rounded hills. These hills con- 
sist of sedimentary, argillaceous sandstones, and the strata present various shades of color, 
changing from white to pink and bluish. Beds of white clay were observed, and layers of 
pebbles. 
Dry creek to the Merced river.—Ten miles from the camp at Mitchell’s bridge, we entered 
the valley of Dry creek ; and I here observed, along its banks, horizontal strata of argillaceous 
sandstone in a soft, unconsolidated state. A house has been built of this soft clayey rock, and 
the blocks have since become hard and stone-like in texture. Outcropping edges of nearly hori- 
zontal beds of compact sandstone, similar to that of the Diablo range at Livermore's pass, were 
. also observed, It is associated with a very coarse conglomerate, or a mass of large pebbles and 
cobble-stones cemented together. These strata appear to be of tertiary age, but no fossils were 
found. 
Merced river, July 21.—Horizontal strata of argillaceous sandstone were observed in descending 
from the plain into the valley of the Merced river. At the time of crossing, the stream was clear 
and pure, and the temperature of the water was found to be 72° F.; air 86. The bed of the 
stream was paved with water-worn boulders, almost all of basaltic and granitic rocks. The 
basaltic fragments were predominant ; and from their quantity and general similarity, I was 
led to conclude that the stream must traverse an extensive region of erupted rock high up in the 
Sierra. 
From the appearance of the bed of this river, and the wide margin of transported rocks, and 
banks of pebbles high above the water at the time we crossed, it is evident that it sometimes 
becomes a rapid and powerful torrent. 
Merced river to Bear creek, July 22, 18.3 miles.—After leaving the Merced our route lay 
among numerous isolated hills with flat summits ; a group of which is represented in outline 
in the figure. 
TABLE HILLS NEAR THE MERCED. 
These hills were estimated to be about one hundred feet in height. They are tormed of hori- 
zontal strata, and are the remnants of a former plain, the intermediate portions having been 
removed by denudation. The “‘ cap rock"' on one of the hills was found to consist of a bed of 
conglomerate, chiefly of quartz pebbles, underlaid by a bed of light-colored sandstone, and a 
FOSSIL TREE. 
second stratum of conglomerate. A cylindrical object, like a log of wood, was protruding two 
feet beyond this layer of sandstone, and it piatt h to bea part of a fossil tree, with a cross sec- 
tion like the figure. 
