J. LeConte—Ancient Glaciers of the Sierras. 333 
and painful falls) The crests of these blades were not continu- 
ous, but irregular both in outline and in trend; very much in 
this respect like ripple-marks or like waves. Again, the 
irregularities in successive blades or waves were so related 
to each other, as to give rise to lighter lines of slope distinctly 
visible at a distance. Thus viewed the two sets of lines were 
related to each other like the lines of an engraved map, the 
blades representing the devel lines, and the lighter lines the lines 
of slope, so that a surveyor had only to copy these in order 
to make a perfect map. 
I was for some time at a loss to account for these blades. I 
sand ripples produced by wind or by currents exhibit also lighter 
lines in the direction of the current, I do not know. 
Ill. Broopy CaNon Guactier. 
The Sierras on their western side slope gradually for 50 or 
60 miles; but on th d y : 
that the plains, 5000 to 7000 feet below the crests, are reached in 
_tono pass is a watershed from which runs a stream in either 
direction. In glacial times it was a snowshed, from which issued 
a glacier in either direction. One of these flowed westward, 
and formed a tributary of Tuolumne glacier, as already ex- 
plained, while the other flowed eastward down the steep incline 
of Bloody Caiion to the level plains of Mono and out on these 
plains for several miles. I know no place where the formation 
‘glacial lakes can be so well studic 
