136 J. LeConte— Ancient Glaciers of the Sierra Nevada. 
which these parallel sey oe were formed. I believe the condi- 
tions were as described b 
We have already given: reason to think that the original 
margin of the lake, in Glacial times, was three or four miles 
back from the present margin, along the series of rocky points 
against which the ridges abut; and that all the flat plain 
thence to the present margin is ‘made land. If so, then it is 
evident that at that time the three glaciers described ran far 
out into the lake, until reaching deep water, where they formed 
icebergs. Under these conditions, it is plain that the pressure 
on this, the subaqueous portion of the glacial bed, would be 
small, and become less and less until it becomes nothing at the 
pon where the icebergs float awa e pressure on the bed 
ing os not enough to overcome the cohesion of ice, there 
would be no spreading. lacier running down a steep narrow 
cation and out into deep water, and forming icebergs at its point, 
would maintain tts slender, tongue-like form, and drop its débris 
on each side, forming parallel ridges, and would not form a ter- 
minal moraine because the materials not dropped previously would 
be carried off by icebergs. In the subsequent retreat of such a 
glacier, imperfect terminal moraines might be formed higher 
up, where the water is not deep enough to form icebergs. It 
is probable, too, that since the melting of the great “mer de 
i and the fo ormation of the lake, the level of the water has 
most remarkable are those formed oody Cafion Glacier, 
in my former paper. These moraines are six 
or seven miles long, 300 to 400 feet nigh, and the parallel 
crests not more than a mile asunder. There, also, as at Lake 
tran nsverse moraines, made duri = the oa 
tinct terraces iad by Whitney* and observed ae don 
sie in glacial times the water stood at feast six hundred feet 
above the present level. In fact, there can be no doubt that at 
that time the waters of Mono Lake (or a much greater body of 
water of which Mono is the remnant) washed against the bold — 
y points from which the débris ridges start. The glaciers 
* Geological Survey of California, vol. i, 451. 
