46 PROCEEDINGS OF THE CALIFORNIA 
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, 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 
point where the icebergs float away. The pressure on the bed being small, 
not enough to overcome the cohesion of the ice, there would be no spreading. 
A glacier running down a steep narrow canon and out into deep water, and form- 
ing icebergs at its point, would maintain its slender, tongue-like form, and drop 
its débris on each side, forming parallel ridges, and would not form a terminal 
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 
glace and the formation of the lake, the level of the water has gone down 
considerably, by the deepening of the Truckee Canon outlet by means of 
erosion. Thus, not only did the glaciers retreat from the lake, but also 
the lake from the glaciers. 
As already stated, similar parallel moraine ridges are formed by the glaciers 
which ran down the steep eastern slope of the Sierras, and out on the level 
plains of Mono. By far the most remarkable are those formed by Bloody 
Cafon Glacier, and described in my former paper. These moraines are six 
or seven miles long, 300-400 feet high, and the parallel crests not more than a 
nile asunder. There, also, as at Lake Tahoe, we find them terminating 
abruptly in the plain without any sign of terminal moraine. But higher up 
there are small, imperfect, transverse moraines, made during the subsequent 
retreat, behind which water “has collected, forming lakes and marshes. But 
observe: these moraines are also in the vicinity of a great lake ; and we have 
abundant evidence, in very distinct terraces described by Whitney,* and 
observed by myself, that in glacial times the water stood at least six hundred 
feet above the present level. In fact, there can be no doubt that at that time 
the waters of Mono Lake (ora much greater body of water of which Mono 
is the remnant) washed against the bold rocky points from which the débris 
ridges start. The glaciers in this vicinity, therefore, must have run out into the 
water six or seven miles, and doubtless formed icebergs at their point, and, 
therefore, formed no terminal moraine there. 
That the glaciers described about Lake Tahoe and Lake Mono ran out far 
into water and formed icebergs, I think is quite certain, and that parallel 
moraines opened below are characteristic signs of such conditions, I also 
think nearly certain. 
f. Glacial Erosion.—My observation on glacial pathways in the high Sierra, 
and especially about Lake Tahoe, have greatly modified my views as to the 
* Geological Survey of California, Vol. I, p. 451. 
