J. LeConte—Ancient Glaciers of the Sierra Nevada. 129 
mirably marked débris ridge (moraine) three hundred feet 
high, four miles long, and one and one-half to two miles apart. 
These moraines may be traced back to the termination of 
the rocky ridges which bound the cafion. On one side the 
moraine lies wholly on the plain; on the other side its upper 
part lies against the slope of Mt. Tallac. Near the lower end 
of the lake a somewhat obscure branch ridge comes off from 
each main ridge, and curving around it forms an-imperfect 
terminal moraine through which the outlet of the lake breaks 
There can be no doubt, therefore, that a glacier once came 
down this cafion filling it 1,000 feet deep, scooped out Fallen 
Leaf Lake just where it struck the plain and changed its angle 
of slope, and pushed its snout four miles out on the level lain, 
nearly to the present shores of Lake Tahoe, dropping its débris 
on either side and thus forming ‘a bed for itself. In its sub- 
Sequent retreat it seems to have rested its snout some time at 
the lower end of Fallen Leaf Lake, and accumulated there an 
Imperfect terminal moraine. The outlines of this little lake 
with its bordering moraines are shown in the diagram-map on 
the nowt page 
9 Cut 
to the lake, and thence close along each side of the lake up to 
the rocky points which terminate the true mountain cafion 
