206 
GEOLOGY. 
apparent when the section was constructed. There is also some douht about the position of the 
outcrop of limestone between stations 191 and 212. It was not possible, in a hurried exami¬ 
nation of such an extended section, to give that attention to measurements and“other observa¬ 
tions upon the rocks which are essential to the truthful representation of plications. 
It is worthy of remark, that here, as in the Appalachians, the most abrupt flexures, as indi¬ 
cated by the dip of the strata, are turned towards the ocean. The dips also indicate that the 
lateral force or wave producing the folding or undulation was from that direction, or from west 
to east. 
In this section of the Sierra Nevada we do not find great masses of clay-slate or roofing 
slates, similar to those of the western slope of the Sierra in the latitude of San Francisco. 
Neither are the talcose or magnesian slates represented, unless the chloritic slates he regarded 
as their equivalents. The entire absence of all erupted dykes of porphyry, or even of ordinary 
trap or greenstone, so far as observed, is also remarkable. There are no indications in con¬ 
nexion with the limestone and quartz rock which throw light upon their age. Whether they 
are Silurian, Devonian, or Carboniferous is yet to he determined. There is some reason to 
regard them as Carboniferous, for these are the nearest known formations of limestone and sand¬ 
stone which are recognizable by fossils. The carboniferous limestone has been recognized by 
Mr. Marcou as far west as the head-waters of the Ha-wil-ha-mook, or Bill Williams’ fork of 
the Colorado, in longitude 113°, or about 350 miles east of these outcrops, and on the same 
parallel of latitude. It is probable that the bed of limestone on the western side of the pass 
is similar in its lithological characters and age to the outcrops on the east, hut its exact rela¬ 
tions to the adjoining rocks were not determined. 
From a consideration and comparison of the different observations, keeping in mind at the 
same time the locality and the peculiar local conditions, I have been induced to regard the pre¬ 
vailing trend of the rocks of the main ridge between stations 125 and 212 as N. 20° to 30° E. 
One great reason for this conclusion is found in the general course of the crest of the ridge, 
which according to the results of the Survey has at that point a northeasterly trend, and it is 
believed to conform in a great measure with the trend of the composing rocks. 
Trend of the granite of the Pass .—Observations upon the trend of the granite were made as 
frequently as possible, and whenever a suitable exposure of the rock was found. In the rough 
canons and steep slopes of the ridges it was not always possible to catch an extended view of 
the outcropping edges of the rocks, and the trends as observed do not in all cases indicate their 
prevailing or predominant direction. The trends that were observed on the western side of the 
ridge were taken on the south side of the creek, and were all west of north, ranging from 5° to 
40°, and one of T2°, hut this is believed to he more westerly in its direction than is common, 
and, possibly, is erroneous. On the eastern side of the crest of the ridge, the trends, with some 
exceptions, were east of north, and were generally regular and well defined. The following are 
some that were noted—a correction of 14° 30' having been applied for variation: 
Station. 
Trend. 
Station. 
Trend. 
176 
N. 14° 30' E. 
203 
N. 300 W . 
183 
N. and S. 
211 
N. 30° 35 ' e. 
191 
N. 15° E. 
212 
N. 39° 30' E. 
202 
N. 150 w. 
