Geology of California. — Turner. 315 
base dikes cut these shales, and during several years' field work 
in the Coast ranges as assistant to Dr. Becker, the writer can 
remember no cases of undoubted dikes of diabase in sedimentary 
rocks containing Cretaceous fossils. 
Supposing Mr. Fairbanks to be correct in considering the Coast 
range metamorphic rocks as pre- Cretaceous in age, it is likewise 
probable that the diabase is also of pre-Cretaceous age. 
The serpentine at mount Diablo, however, was clearly shown to 
have been intruded as a dike into the Knoxville shales which, like 
the dike, stand vertical and contain specimens of Aucella on either 
side of the dike. 
There is therefore no doubt of the post-Knoxville age of some 
of the serpentine of the Coast ranges. Mr. Fairbanks seems like- 
wise of the opinion that the serpentine of the Coast ranges is of 
post-Knoxville age, having obtained evidence of this in Tehama 
and Colusa counties (see p. 164 of his paper). 
The gabbro described in the bulletin on mount Diablo above 
referred to as occurring in Bagley creek appears to be a dike in the 
Knoxville shales which contain Aucella on both sides of the dike. 
This gabbro was thought to be connected genetically with the 
P3'^roxenite-serpentine area shown on the geological map. It is 
probable, therefore, that some of the gabbro of the Coast ranges 
is post-Knoxville in age. 
Professor Whitney came to the conclusion that the silicified 
shales or phthanites at mount Diablo passed over into the unalter- 
ed Knoxville shales which contain Aucella. The best proof of this 
would be to find the Aucella in the silicified shales, and this maj' 
well be possible, for while these rocks have been thoroughly im- 
pregnated with silica and then broken up, and re-cemented by 
silica they have not been subjected to such pressure as to be ren- 
dered schistose. Mr. Lindgren found in microscopic sections 
organic forms which wei-e considered by professor Leidy probably 
to be tests of Foraminifera, and these tests, though silicified, 
retain their spherical form. So far as known to the writer, no 
moUuscan shells have been found in the silicified shales. 
If the Knoxville beds are deposited unconformabl}' on the 
Coast range metamorphic series, it is certain that the basal mem- 
bers of these beds would contain the debris of the metamorphic 
series. Mr. Fairbanks appears to have noted nothing on this 
point. 
