certain regions on the surface of the earth that are actually rainless;
and it is these which present us with the true and real contrast to the
luxuriant vegetation and teeming life of the country of the Amazon. In
these rainless regions all is necessarily silence, desolation, and
death. No plant can grow; no animal can live. Man, too, is forever and
hopelessly excluded. If the exuberant abundance of animal and vegetable
life shut him out, in some measure, from regions which an excess of heat
and moisture render too prolific, the total absence of them still more
effectually forbids him a home in these. They become, therefore, vast
wastes of dry and barren sands in which no root can find nourishment,
and of dreary rocks to which not even a lichen can cling.

The most extensive and remarkable rainless region on the earth is a vast
tract extending through the interior and northern part of Africa, and
the southwestern part of Asia. The Red Sea penetrates into this tract
from the south, and thus breaks the outline and continuity of its form,
without, however, altering, or essentially modifying its character. It
divides it, however, and to the different portions which this division
forms, different names have been given. The Asiatic portion is called
Arabia Deserta; the African tract has received the name of Sahara; while
between these two, in the neighborhood of Egypt, the barren region is
called simply _the desert_. The whole tract is marked, however,
throughout, with one all-pervading character: the absence of vegetable,
and, consequently, of animal life, on account of the absence of rain.
The rising of a range of lofty mountains in the center of it, to produce
a precipitation of moisture from the air, would probably transform the
whole of the vast waste into as verdant, and fertile, and populous a
region as any on the globe.

[Illustration: VALLEY OF THE NILE]