pipe cheerily in the shallows, soon
followed by the ouzel, which is the first bird to visit a
glacier lake, as the sedge is the first of plants.
So the young lake grows in beauty, becoming more and more
humanly lovable from century to century. Groves of aspen
spring up, and hardy pines, and the hemlock spruce, until it
is richly overshadowed and embowered. But while its shores
are becoming enriched, the soil-beds creep out with incessant
growth, contracting its area, while the lighter mud-particles
deposited on the bottom cause it to grow shallower, until at
length the last remnant of the lake vanishes,--closed forever
in ripe and natural old age. And now its feeding-stream goes
winding on without halting through the new gardens and groves
that have taken its place.

The length of the life of any lake depends ordinarily upon the
capacity of its basin, as compared with the carrying power of
the streams that flow into it, the character of the rocks over
which these streams flow, and the relative position of the
lake toward other lakes. In a series whose basins lie in the
same canyon, and are fed by one and the same main stream,
the uppermost will, of course, vanish first unless some other
lake-filling agent comes in to modify the result; because at
first it receives nearly all of the sediments that the stream
brings down, only the finest of the mud-particles being
carried through the highest of the series to the next below.
Then the next higher, and the next would be successively
filled, and the lowest would be the last to vanish. But this
simplicity as to duration is broken in upon in various ways,
chiefly through the action of side-streams that enter the
lower lakes direct. For, notwithstanding many of these side
tributaries are quite short, and, during late summer, feeble,
they all become powerful torrents in spring-time when the
snow is melting, and carry not only sand and pine-needles, but
large trunks and bowlders tons in weight, sweeping them down
their steeply inclined channels and into the lake basins with
astounding energy. Many of these side affluents also have
the advantage of access to the main lateral moraines of the
vanished glacier that occupied the canyon, and upon these they
draw for lake-filling material, while the main trunk stream
flows mostly o