s brought down by glaciers north of this point. The long
moraines of these glaciers are plainly visible from the Lake
surface; but I have not examined them. Thus, all the land, for
three or four miles back from the Lake-margin, both north and
south of Rubicon Point, is composed of _confluent glacial
deltas_, and on these deltas the moraine ridges are the
_natural levees_ of these ice-streams.

_e. Parallel Moraines_. The moraines described above are
peculiar and almost unique. Nowhere, except about Lake Tahoe
and near Lake Mono, have I seen moraines in the form of
_parallel ridges_ lying on a level plain and terminating
abruptly _without any signs of transverse connection
(terminal moraine) at the lower end_. Nor have I been
able to find any description of similar moraines in other
countries. They are not terminal moraines, for the glacial
pathway is open below. They are not lateral moraines, for
these are borne on the glacier itself, or else stranded on the
deep canyon sides. Neither do I think moraines of this kind
would be formed by a glacier emerging from a steep
narrow canyon and running out on a level plain; for in such
cases, as soon as the confinement of the bounding walls is
removed, the ice stream spreads out into an _ice lake_.
It does so as naturally and necessarily as does water under
similar circumstances. The deposit would be nearly transverse
to the direction of the motion, and, therefore, more or less
crescentic. There must be something peculiar in the conditions
under which these parallel ridges were formed. I believe the
conditions were as described below.

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 point where the icebergs float away. The
pressure on the bed being small, not enoug