GEOLOGY OF THE SOUTHERN COAST RANGES 575 
slowly. Peculiar conditions must have existed, the sea being 
practically free from detrital material though the area of depo- 
sition could not have been far removed from the land. 
The latest igneous action in this region probably followed 
the initial folding of the Monterey series preceding the deposi- 
tion of the San Pablo formation, when the basalt, teschenite, 
and olivine diabase appeared. 
After a period of elevation and prolonged erosion during 
which the great thickness of Monterey series was totally 
removed from some areas, and the shales of that period had 
undergone a chemical change, a subsidance began and the sandy 
strata of the San Pablo formation were laid down. The present 
configuration did not exist and this formation probably spread 
across the Santa Lucia range. 
The discovery of the nonconformity of the San Pablo forma- 
tion upon the bituminous shales (Monterey series) necessitates 
the addition of a correction to the diagram recently published 
illustrating the oscillations of the Coast Ranges.*. Two oscilla- 
tions should appear where the one is represented as separating 
the Miocene and Pliocene, with the understanding that the 
dividing line between these two periods is not at present settled. 
After a deposition of at least 3000 feet of sediments, ‘eleva- 
tion and folding were experienced, terminating the San Pablo 
period; and the outlines of the present mountains were origi- 
nated. 
Marine formations of late Neocene age havé not with cer- 
tainty been recognized in this region. The Paso Robles forma- 
tion indicates the existence of fresh-water lakes of large extent. 
With the close of the Neocene an upward movement was inau- 
gurated and continued, it is believed, until the region was much 
higher than at present. 
Following this early Pleistocene elevation a reversal took place 
and sinking went on until the coast was submerged to the depth 
of the highest terraces. With the gradual recovery from this 
depression the lower terraces were formed and again a point 
* American Geologist, Vol. XX, p. 225. 
