212 ELEMENTARY GEOLOGY 
and extensive than now (Fig. 116). From this we 
Fie. 116. 
A map of a part of the Sierra of Cali- 
fornia, showing former extent of val- 
ley glaciers. Existing glaciers marked 
black. 
may fairly infer that there 
has been some change in 
climate. | 
The evidence of this 
is (1) the presence of 
smoothed and _ grooved 
rocks, (2) bowlders whose 
original home was higher 
up in the mountains, and 
(5) moraines (medial, lat- 
eral, ground, and termi- 
nal), now resting in the 
valley bottom, where they 
were left when the ice 
melted. Where hillocks 
of morainal debris are 
‘stretched across the course 
of streams, lakes are 
present (Fig. 117), as they 
are also in basins of rock, 
which the ice appears to 
have gouged out. This 
evidence is in harmony 
with that which has led 
us to believe that North America and Europe were 
recently the scene of extensive ice action, when a 
