J. LeConte—Ancient Glaciers of the Sierras. 337 
VI. American River GLactirr. 
On returning homeward we retraced our steps southward up 
Lake valley for about 8 miles, then crossed the western crest of 
the Sierras by Johnson’s pass, and then-went down the cafion 
of the south fork of the American river. 
mong the tributaries which flowed into Lake valley gla- 
cier, one of the largest came down from Johnson's pass. ‘Th 
scored, polished, moutonnéed surfaces were very conspicuous 
and beautiful. From the same pass another much greater gla- 
These have been smoothed and scored on every side in the 
most perfect manner. One of these is the ‘“ Sugar-loaf’ rock,” 
from which the village takes its name. 
Four or five miles below this point, glacial marks disappear, 
and the cafion changes its character. The upper part of the 
Cafion consists of a succession of broad level meadows ; the 
lower part is sharply V-shaped, and contains no longer any 
meadows. The change marks, I believe, the distinction 
between glacial and river erosion. This change, however, marks 
Uso the change from granite to slate. Glaciers may have 
passed still lower down the cafion; but if so the glacial form of 
the cajion has been greatly modified by water-erosion, whic 
has cut far below the glacial bed. 
VII. Some GENERAL REFLECTIONS. 
a and Washington territory: in other words, its general 
rection was southward and seaward. We have given 40° as 
about the southern margin; but from this southern margin the 
general ice-sheet stretched out finger-like prolongations still 
farther south down the valleys, in the form of separate glaciers. 
The O serete of many of these separate glaciers have been 
traced by eastern observers. There can be no donbt, however, 
