The Geology of the Coast Ranges. — Lavson. 351 
lenses. A detailed petrographical description of a typical 
occurrence of this serpentine has been given by Mr. Palache* 
and another occurrence has been investigated by Mr. 
Ransomef. Other occurrences have been petrographicallj'^ 
examined by the writer with the same general result that 
they are referable to original olivine pyroxene rocks or to 
pyroxenites without olivine. 
There are no other serpentines on the peninsula, nor, in 
the experience of the writer, elsewhere in the Coast ranges, 
which are not the alteration of products of intrusive perl- 
dotites or pyroxenites. 
The serpentines are of later age than the basaltic and dia- 
basic intrusives. 
Silica-Carbonate Sinter. — This is a very curious rock which 
is somewhat characteristic of portions of the Coast ranges. It 
is a rusty,cellular-weathering mixture of opal and chalcedony 
with the carbonates of lime, magnesia and iron. It occurs in 
the San Francisco sandstone, and although not extensively de- 
veloped on the peninsula, it occurs in considerable sheets in 
Aucella bearing sandstone in other portions of the ranges. It 
appears to be a chemical deposit, and its occurrence in exten- 
sive sheets roughly parallel with the bedding suggests that it 
is a contemporaneous deposit, but it may possibly be a vein 
formation. Its occurrence in the Aucella sandstones elsewhere 
and in the San Francisco sandstones of the peninsula is of in- 
terest as a possible factor in the correlation of these forma- 
tions. 
Metamorphic Schists. — These rocks although not extensively 
developed on the peninsula, are believed to be petrographi- 
cally and genetically representative of the crystalline schists 
of the same series of rocks throughout the Coast ranges. Thej'^ 
are chietiy glaucophune, hornblende or mica schists, with or 
without garnets and other accessory minerals. Quartz or 
feldspar, or both, are usually present. These metamorphic 
schists have a very limited distribution and this has a definite 
relation of dependence upon the occurrence of the intrusive 
peridotites and other basic irruptives. The schists are only 
known in the vicinity of these intrusives, and are frequently 
*Bull. Dept. Geol. Univ. Cal., vol. i, no. 5. 
fLoc. cit. 
