354 The American Geologist. June, 1895 
of the series as studied on the San Francisco peninsula may 
be very briefly summarized. As regards the volume of the 
series, the writer is not yet prepared to make any explicit 
statement, as the faulting of the region renders an estimate 
difficult. It is safe to say, however, that the series is several 
thousand feet thick. This volume of strata is folded gener- 
ally in open, rather flat synclines and anticlines. In the 
southern part of the field, however, where the strata have 
been crowded up against the Montara granite, the folds are 
locally sharply compressed and at least one dominant syncline 
shows pronounced reversed dips. Faults are important feat- 
ures of the structure, but they are difficult to measure. 
Intense crushing is not a feature of the series, except locally 
where softer beds have been affected. Locally, also, intense 
plication occurs in the thin bedded radiolarian charts by 
reason of the ease with which these hard, brittle beds have 
moved on the shaly partings. 
Tertiary Rocks. 
Near Spanishtown, a little to the south of Lat. 87° 30', 
sandstone supposed to be of Tejon age and the white siliceous 
shales of the Monterey series (Miocene) repose indifferently 
on the Montara granite and upon the Franciscan series 
unconformably. The relations are such as to indicate clearly 
a great interval of erosion between the close of the Franciscan 
sedimentation, and the deposition of the Tertiary strata. 
After the Miocene, a period of erosion intervened which 
removed the whole of the earlier Tertiary rocks from a large 
part of the region for we find a great thickness of Pliocene, 
Merced series, reposing on the Franciscan rocks and on the 
granite. This Merced series has been noticed in a former 
paper.* As has been shown there, the strata of this series to 
the thickness of over one mile are magnificently exposed in 
the sea-cliff south of the city of San Francisco and dip contin- 
uously throughout the section to the northeast. Since their 
deposition these Merced rocks have been profoundly affected 
by diastrophic movements and have been denuded from a 
large portion of the peninsula over which they were once 
spread. 
*P>ull. Uept. Geol. Univ. Cal., vol. i, no. 4. 
