60 
GEOLOGY. 
into black. The slaty structure is well developed, and the cleavage is facile ; smooth, flat sur¬ 
faces being readily obtained. A fresh cleavage surface presents a silvery lustre, produced by 
thin films of mica. The composition of the rock, when critically examined, appears to be 
chiefly quartz and mica ; the latter being in exceedingly thin films, and never showing broad 
plates or cleavable folia. The two minerals are so intimately blended that it is almost impos¬ 
sible to obtain a view of either in an isolated condition. The rock has a strong argillaceous 
odor when breathed upon, and portions of it appear to have contained minute disseminated 
grains of sulphuret of iron, which, by its decomposition, has left minute stains of sesquioxyde of 
iron. Chlorite, or a chrome-green mica, is sparingly distributed in some parts of the rock; 
especially near quartz veins and seams, which abound in all parts of the ridge. 
In a large accumulation of debris, in a canon leading from the higher part of the ridge, I 
found many masses in which talc was a principal ingredient, and was closely associated with 
cellular quartz. They were evidently portions of veins that had contained iron pyrites, and 
they much resembled specimens from the auriferous slates of North Carolina. The talcose 
minerals appeared to be the most abundantly developed in the vicinity of, or in contact with, the 
quartz veins. Similar conditions are found in the Carolinas. 
This ridge of slate rock is remarkable for its even bedding or stratification. The planes of 
bedding are perfectly flat, and without flexures or distortions. The laminae are as thin as paper, 
and lie closely together like the leaves of a book; yet the rock is firm and very hard, and thin 
plates are not very easily separable. The dip, also, is very regular, at about the same angle, 
even at distant points. This dip, being northerly, is towards the main ridge of granite ; the 
rock, however, does not appear on the opposite side of the valley, adjoining the granite ; or if 
it does, its structure is entirely destroyed by metamorphic action. It is probable that further 
south, between this slate ridge and the valley of the Santa Clara, there is granitic rock, perhaps 
eruptive, like that at the summit. This I was not able to verify, as our examination did not 
extend to the open valley. ' I afterwards found granitic and highly metamorphosed rocks in the 
lower portions of the new pass adjoining, and this leads me to the conclusion that these auriferous 
slates cover the northern flank of a granitic ridge, and dip from it. 
Gold .—As the appearance of both the rocks and the quartz veins indicated the presence of 
gold, I was induced to make several trials of the earth at favorable points in the bed of the creek. 
Several pans of gravel and black sand, from different places, were washed out, without obtain¬ 
ing the “ color.” I am informed that there are rich placers not far from the rancho of San 
Francisquito. These are said to have been worked by Mexicans in 1840, and abandoned in 
1849, when the reports of the great discoveries of gold on the Sacramento river were received. 
The favorable indications for gold in this vicinity are sufficient to warrant a more thorough and 
extended examination than it was possible for me to give. 1 
It was interesting to observe how completely the direction of the creek was modified by the 
ridges of slate. The bends of the stream, instead of being rounded curves, make sudden and 
angular turns around the sharp edges of the strata, and flow in nearly straight lines between 
these points, conforming to the-direction or trend of the rock. 
The topographical features and the variations of the scenery, in this pass, change with its 
1 Since the above -vvas written, considerable excitement has been produced by the working of placers in this district, on 
the Santa Anna river. The accounts have been conflicting and unsatisfactory, but that very considerable deposits of gold 
exist is proved beyond doubt. A specimen of this gold, which I have recently received, is in fine, irregular grains, inter¬ 
mediate in size between ordinary scale or river gold and that from the “dry diggings.” It is of good quality, comparing 
favorably with the best gold of the Sierra Nevada gold field. August, 1855. 
