the greatest depression the sites of the central chains of the
Rockies were probably islands, but early in the period they may
have been connected with the broad lands to the south and east.
Thousands of feet of Carboniferous sediments were deposited where
the Sierra Nevada Mountains now stand.

THE PERMIAN. As the Carboniferous period drew toward its close the
sea gradually withdrew from the eastern part of the continent.
Where the sea lingered in the deepest troughs, and where inclosed
basins were cut off from it, the strata of the Permian were
deposited. Such are found in New Brunswick, in Pennsylvania and
West Virginia, in Texas, and in Kansas. In southwestern Kansas
extensive Permian beds of rock salt and gypsum show that here lay
great salt lakes in which these minerals were precipitated as
their brines grew dense and dried away.

In the southern hemisphere the Permian deposits are so
extraordinary that they deserve a brief notice, although we have
so far omitted mention of the great events which characterized the
evolution of other continents than our own. The Permian fauna-
flora of Australia, India, South Africa, and the southern part of
South America are so similar that the inference is a reasonable
one that these widely separated regions were then connected
together, probably as extensions of a great antarctic continent.

Interbedded with the Permian strata of the first three countries
named are extensive and thick deposits of a peculiar nature which
are clearly ancient ground moraines. Clays and sand, now hardened
to firm rock, are inset with unsorted stones of all sizes, which
often are faceted and scratched. Moreover, these bowlder clays