Oscillations of the California Coast. — Fairbanks. 225 
eel to show that at the time of this latter disturbance these 
beds were folded beneath the sea, and that the erosion pre- 
ceding the formation of the terraces was due solely to wave 
action, for wave action must have been carried on at the level of 
the sea, and after truncation, unless there was subsidence, there 
would have been no opportunity for the terrace formations, 
sometimes 100 to 300 feet thick, to have been left unmodified 
and unconformable upon the Pliocene, which as a matter of 
fact we find to be the case almost everywhere. 
PosT-MiocENE Uplift. 
There seems to be no question in the minds of geologists 
concerning the post-Miocene disturbance and uplift. By many 
it has been believed that the Coast Ranges originated at this 
time, but this, as I have shown in other papers, is clearly an 
erroneous conception, as the records of several stratigraphic 
breaks are visible in the older rocks of this region. It is very 
probable that the post-Jurassic disturbance elevated the coast 
so that the present islands were connected with the mainland 
and much of the submarine plateau exposed. As yet we know 
in only a general way the effects of the post-Miocene disturb- 
ance, but I believe that there are good reasons for assuming 
that the uplift was very marked and that the shore line was 
forced out some distance beyond the present one, probably tak- 
ing- in the submarine plateau. The Miocene is everywhere over- 
laid unconformably by the later formations. The valleys or- 
iginating with the post-Miocene uplift, due partly to struct- 
ural conditions, and ])artl3'' to erosion, were more or less filled 
with sediments during the Pliocene submergence. With the 
early Pleistocene elevation they were again cut out, and filled 
during the following depression with the terrace deposits. As 
a result of this sequence it becomes difficult always to cor- 
rectly discriminate and refer any particular phenomena of 
erosion to its true source. If we were in the possession of 
more records of deep borings in the mouths of the large val- 
leys opening out upon the coast the question might more easily 
be settled. It is very evident however from the character of 
many of the larger valleys where the Pliocene reposes uncon- 
formably upon the Miocene that this relation extends below 
the present level of the sea. If this is the case these Miocene 
valley's are not simply of structural origin, and subsequentlj'^ 
