54 OSCAR HV HERSH EY: 
DISCUSSION OF CLIMATIC CONDITIONS DURING GLACIATION 
It goes without saying that it was cold and there was much 
snow. But under this heading I wish to argue that there was 
no difference in the character of the climate between that and 
now—merely a lowered annual temperature and _ probable 
increased snowfall. The present climate of the Sierra Costa 
Mountains partakes of the general equability of the Pacific Coast 
region, but in addition possesses a typical alpine character. A 
strong contrast between the heat of night and day, and between 
that of light and shadow, is a characteristic of high altitudes where 
the atmosphere is clear and light, and radiation rapid. One 
may suffer from the heat in toiling up a sunny slope, while the 
air in the shadow of a peak may seem almost freezing cold. 
This is the condition of today at the higher levels of the Sierra 
Costa Mountains, and the behavior of the glaciers indicates that 
the same obtained in their time. They were unusually sensitive 
to sunlight, and shrank into the shadow of the peaks. 
Gulches which faced the sun were unglaciated, altho perhaps 
surrounded by others in which ice accumulated to a depth of 
over 1000 feet. In fact, shadow was as much one of the neces- 
sary conditions of glaciation as cold and snow fall. This shows 
that the climate possessed the same alpine character as today. 
I am strongly impressed that the evidence indicates an altitude 
for these mountains during the Wisconsin epoch, at least as 
great as the present. 
A POSSIBLE CAUSE OF THE GLACIAL PERIOD IN THE SIERRA COSTA 
MOUNTAINS 
I am not prepared to argue conclusively as to why these 
glaciers formed in the elevated valleys of the northwestern Cali- 
fornia mountains; but I wish to present, in closing this paper, 
what I conceive to be a possible explanation of their existence, 
an hypothesis sufficient to account for all their phenomena. 
The valleys where the ice accumulated are all above 6000 
feet of altitude, and the sites of the main mévés approximate a 
general elevation of 6500 feet above the sea. Even today the 
