162 The American Geologist. March, 1892 
must have been concerned in the upheaval of rocks of that age 
in Shasta county. Portions of the metamorphic rocks of the 
Coast Range bear the closest resemblance to those of the gold 
belt of the Sierras, which were considered by Prof. Whitney to 
be not younger than the Jurassic. Dr. Becker has affirmed that 
the gold bearing rocks of the Sierras are in part Neocomian on 
account of the presence of a species of Aucella indistinguishable 
from one found in the Coast Ranges.* He reaches the conclu- 
sion that the Knoxville and Mariposa beds are of the same age, T 
including of course the metamorphic rocks of the Coast Range 
in the Knoxville. In speaking of the Coast Ranges as members 
of the western Cordillera system he says, ‘The earliest determin- 
able portion of the Coast Ranges must therefore be considered as 
due to the same disturbance which added the gold belt proper to 
the Sierra Nevada.” And again an important uplift of the 
Sierra Nevada was contemporaneous with the first known up- 
heayal of the Coast Ranges. 4 
Laying aside the conclusion reached by Dr. Becker concerning 
the occurrence of the Aucella in the Sierra Nevada, I fully agree 
with him in regard to the simultaneous upheaval of the two series 
of ranges, and that they belong to the same mountainsystem, and 
finally, that whatever can be proved to be true of the metamor- 
phies of the Coast Ranges, with reference to the points under 
discussion, must also be true of the rocks of which the Mariposa 
beds form a part. 
Granted now a pre-Cretaceous age for the rocks of the Coast 
Ranges, and their upheaval as contemporaneous with that of the 
Mariposa beds, we must, as a consequence postulate a pre-Cre- 
taceous age for the Mariposa beds. These beds are an integral 
part of the Sierras and consist largely of black slate. I have 
traced them almost continuously for a distance of a hundred and 
twenty miles and found them enclosed in a great width of other 
metamorphic rocks. The upheaval of the whole was accom- 
panied by an extrusion of granite well illustrated a few miles 
southwest of Mariposa, where the black slates abut against the 
*Geol. of the Quicksilver Deposits, p. 201. 
+Geol. of the Quicksilver Deposits, pp. 195-198. 
tGeol. of the Quicksilver Deposits, p. 211. 
S$Geol. of the Quicksilver Deposits, p. 212. 
