The Geology of the Coast Ranges. — Latrson. 345 
fected the field and which have all contributed to and been 
part of the process of evolution of this modern geomorphy is 
astonishingly incisive and complex. 
Crystalline Limestone. 
Only a very small remnant of this formation occurs within 
the limits of our field, although it is extensively developed, 
in a similar relation to the same granite as that of Montara, 
in the Santa Cruz mountains to the south. The marble occurs 
as a small patch on the southwest side of Pilarcitos canon 
below the stone dam, and is either a large inclusion in the 
granite or is a portion of the formation which once arched 
over the intrusive mass. It is very clearly a remnant of a pre- 
granite formation which was invaded by the granite batholite. 
Like many other marbles associated with the granites of the 
southern Coast ranges, it is charged with scales of graphite. 
Montara Granite, 
The granite constitutes the mass of the bold mountainous 
ridge which rises abruptly from the shore in the southwestern 
part of the peninsula to an elevation of nearly 2,000 feet. It 
forms an oval area whose major axis is ten miles in length 
and has a northwest and southeast trend parallel to the gen- 
eral trend of the Coast ranges. It extends from point San 
Pedro to a little beyond the pass above Crystals Springs lake. 
The maximum transverse diameter of the area is four miles. 
The granite is in general a coarse gray, hornblende-biotite 
granite, hornblende preponderating. Locallj'' the biotite is 
the chief dark constituent. Various subordinate facies of 
the rock occur. These are due to the relative proportions in 
which the essential constituents appear, the occasional por- 
phyritic character of the hornblende, the local abundance of 
the accessory constituent titanite, and the deformation of the 
rock by shearing action, resulting in rude foliation associated 
with the development of secondary biotite from the hornblende. 
The prevalent facies is very quartzose and has plagioclase ap- 
parently^ not less abundant than orthoclase. In various parts of 
the mass basic secretions appear in the form of dark patches. 
Pegmatitic and aplitic dikes traverse the mountain in all 
possible directions, sometimes in well defined fissures, some- 
times in exceedingly irregular intrusions. The aplites and 
pegmatites are not sharply separable but may grade into one 
