332 
The American Geologist. 
May, 1*96 
4. A formation of light colored sandstone which is supposed, doubt¬ 
fully, to be of Tejon {Eocene) age. 
5. The Monterey series {Miocene). 
6. The Merced series {Pliocene). 
7. The Terrace formations , Pleistocene and later. 
Prof. Lawson’s descriptions show that there are at least two distinct 
horizons of limestone in the region under discussion,—a crystalline 
limestone that has been invaded by the granite (Gavilan limestone?) 
and a foraminiferal limestone which is interbedded with the rocks of 
the Franciscan series. It is accordingly a pure assumption to denomi¬ 
nate all the limestone of the region as the “ Gavilan limestone ” and 
speak of it as though it were a single originally continuous bed, as is 
done by Mr. Ashley. 
The San Francisco sandstone is described by Prof. Lawson as being 
the dominant sedimentary formation of the Franciscan series, and being 
interbedded with the foraminiferal limestone and radiolarian chert. A 
similar usage was followed by the writer of the present criticism in two 
earlier papers,* in the former of which the revival of Blake’s old name 
was proposed. It is a matter of comparatively small import whether 
Blake did or did not originally include with this sandstone certain beds 
which later turned out to be Miocene, or that he referred the whole of it 
to the Tertiary. The fact remains that the term is an excellent one for 
the designation of a great mass of sandstones which are distinctly pre- 
Miocene but whose exact age is not yet fixed, and it possesses moreover 
the advantage of priority. The whole Franciscan series, according to 
Prof. Lawson, is separated from the lowest known Miocene by a long 
erosion interval, j - Much of the sandstone which the writer of the pa¬ 
per before us has placed within his “Pescadero series’’ upon cursory 
field examination, such for example as the sandstone of Telegraph hill 
in the city of San Francisco, undoubtedly belongs with this older pre- 
Miocene series. Detailed field study and mapping of the Coast ranges 
teaches nothing more emphatically than that the correlation of the 
sandstones over any considerable area by superficial lithological resem¬ 
blances is utterly futile. 
In brief then, the “Metamorphics” of our author, duly corrected as 
regards the “Gavilan limestone,” and increased by a portion of his 
“Pescadero series” corresponds with the well defined Franciscan series 
of Lawson. 
Passing upward in the “ Pescadero series” through unfossiliferous 
sandstones which may possibly be Eocene (compare No. 4 of Prof. 
Lawson’s seven terranes), we reach, near the top, heavy beds of con¬ 
glomerate containing Miocene fossils. This conglomerate is said to be 
made up of pebbles from the “Metamorphics,” whose presence, as 
Mr. Ashley admits, it is not easy to account for “ unless we assume 
considerable erosion previous to their laying down.” As the conglomer¬ 
ates and underlying sandstones are apparently conformable in the cliff 
*Bull. Dept. Geol. Univ. of Calif., vol. I, pp. 71-114 and 193-240. 
|Am. Geologist, vol. xv, p. 354. 
