4 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
Mr. J. S. DILLER communicated 
NOTES ON THE GEOLOGY OF NORTHERN CALIFORNIA. 
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[ Abstract. ] 
Under the direction of Capt. Dutton I have spent the last three 
summers studying the geology of northern California and the ad- 
jacent portion of Oregon. The conclusions of a general nature 
referring to that region may be briefly summarized as follows: 
In the northern end of the Sierra Nevada and the central por- 
tion of the Coast range, among the highly plicated, more or less 
metamorphosed strata which are older than those of the Chico group, 
there appears to be but one horizon of limestone, and that is of Car- 
boniferous age. 
The northern end of the Sierra Nevada is made up of three 
tilted orographic blocks which are separated from each other by 
great faults. The westernmost of these blocks stretching far to the 
southeast appears to form the greater portion of the range. 
As in the Great Basin region the depressed side of each block 
was occupied by a body of water of considerable size. The deposits 
formed in these lakes gave rise to the fertile soils of American and 
Indian valleys. 
The plication of the strata in the Sierra Nevada range took place, 
at least in great part, about the close of the Jurassic or beginning 
of the Cretaceous period, but the faulting which really gave birth 
to the Sierra as a separate and distinct range by differentiating it 
from the great platform stretching eastward into the Great Basin 
region, did not take place until towards the close of the Tertiary or 
the beginning of the Quaternary. 
Although the faulting may have commenced earlier, the greater 
portion of the displacement has taken place since the deposition of 
a large part of the auriferous gravels and the beginning of the 
great volcanic outbursts in the vicinity of Lassen’s Peak. If we 
may accept numerous small earthquake shocks as evidence, the 
faulting still continues. 
The distribution of the rocks of the Chico group indicates that 
the western coast of the continent at that time lay along the western 
base of the Sierra extending around the northern end of the range 
in the vicinity of Lassen’s Peak and stretching far northeasterly 
into Oregon. Off the coast lay a large island which now forms 
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