ntal sandstones with beds of chert and
water-worn quartz pebbles. This latter formation extends as far as Mount
Hopeless, where the slate ranges of South Australia rise abruptly from
the plain. The sandy deserts and mud plains are only superficial
deposits, as the sandstones are often exposed where the upper formation
is intersected by gullies. The direction of the parallel ridges of drift
sand appear to be the result of the prevailing winds, and not the action
of water, it being sufficient to visit them on a windy day to be
convinced that it is unnecessary to seek for a more remote and obscure
cause than that which is in present operation. It is, perhaps, with
reference to the physical geography of Australia that the results of the
Expedition are most important; as by connecting successively the
explorations of Sir T. Mitchell, Mr. Kennedy, Captain Sturt, and Mr.
Eyre, the waters of the tropical interior of the eastern portion of the
Continent are proved to flow towards Spencer's Gulf, if not actually into
it, the barometrical observations showing that Lake Torrens, the lowest
part of the interior, is decidedly above the sea-level. Although only
about one-third of the waters of Cooper's Creek flow into Lake Torrens by
the channel of Streletzki Creek, there is strong evidence that the
remaining channels, after spreading their waters on the vast plains which
occupy the country between them and Sturt's Stony Desert, finally drain
to the south, augmented probably by the waters of Eyre's Creek, the Stony
Desert, and perhaps some other watercourses of a similar character coming
from the westward. This peculiar structure of the interior renders it
improbable that any considerable inland lakes should exist in connection
with the known system of waters; for, as Lake Torrens is decidedly only
an expanded continuation of Cooper's Creek, and therefore the culminating
point of this vast system of drainage, if there was sufficient average
fall of rain in the interior to balance the effects of evaporation from
the surface of an extensive sheet of water, the Torrens Basin, instead of
being occupied by salt marshes, in which the existence of anything beyond
shallow lagoons of salt-water is yet problematical, would be maintained
as a permanent lake. Therefore, if the waters flowing from so large a
tract of country are insufficient to meet the evaporation from the
surface of Lake Torrens, there is even less probability of the waters of
the