m of the adjoining portions
of the gulf. The rapidly growing delta crept southward and westward
into the gulf. As fast as the sediment was built up above the reach
of the tide, vegetation appeared, which, retarding the flow of
the water at times of flood, aided the deposition of silt and the
building up of the delta.

As the centuries went by, these lowland plains became more and
more extensive, until the gulf was actually divided into two parts
by the spreading of the delta across to the western shore. The
portion of the gulf thus cut off from the ocean formed a salt lake
fully one hundred miles in length.

We may suppose that for a long time before the barrier was high
and strong, the tidal currents occasionally broke over the delta
and supplied the lake with water. As the river meandered here and
there over the flat delta, its channels must have undergone many
changes at every time of flood. A part of the water without doubt
flowed into the salt lake, and another portion into the open gulf.
In fact, the basin in which the lake lay, now known as the Colorado
desert, continued to receive water from the river, at intervals,
until very recently. In 1891 an overflow occurred, through the
channel known as New River, which flooded the lower portion of the
basin and threatened to cover the railroad.

When the ocean had been permanently shut off from the head of the
gulf, and the river itself had been largely diverted toward the south,
the lake began to dry up. At last, most of the water disappeared
and there remained a vast desert basin, at its greatest depth two
hundred and fifty feet below the level of the ocean. In the bottom
of the basin a bed of salt appeared, for this substance could not
be carried away, as the water had been, by the thirsty air.

Remarkably perfect beaches still exist around the shores of this
old lake, and on them are found the pearly shells of multitudes
of fresh-water mollusks. The presence of these shells leads us to
believe that after the salt lake dried up, the river again broke
in and formed a new lake of comparatively fresh water which also,
after a time, dried up.

The wonderful fertility of the Colorado delta is just beginning
to be appreciated. Canals have been dug to take the water from the
river and distribute it over the land. Year by year the cultivated
lands are being extended. The change which irrigation is making
upon the surface of one of the worst deserts in the country is