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it is fully fifteen hundred miles long, and in some places a thousand in
breadth, its surface-extent is probably not over one million of square
miles, or twenty-five times the size of England. Fancy a desert
twenty-five times as big as all England! Do you not think that it has
received a most appropriate name when it is called the _Great American
Desert_?

Now, my young friend, what do you understand by a desert? I think I can
guess. When you read or hear of a desert, you think of a vast level
plain, covered with sand, and without trees, or grass, or _any_ kind of
vegetation. You think, also, of this sand being blown about in thick
yellow clouds, and no water to be met with in any direction. This is
your idea of a desert, is it not? Well, it is not altogether the
correct one. It is true that in almost every desert there are these
sandy plains, yet are there other parts of its surface of a far
different character, equally deserving the name of _desert_. Although
the interior of the great Saara has not been fully explored, enough is
known of it to prove that it contains large tracts of mountainous and
hilly country, with rocks and valleys, lakes, rivers, and springs.
There are, also, fertile spots, at wide distances from each other,
covered with trees, and shrubs, and beautiful vegetation. Some of these
spots are small, while others are of large extent, and inhabited by
independent tribes, and even whole kingdoms of people. A fertile tract
of this kind is called an oasis; and, by looking at your map, you will
perceive that there are many oases in the Saara of Africa.

Of a similar character is the Great American Desert; but its surface is
still more varied with what may be termed "geographical features."
There are plains--some of them more than a hundred miles wide--where you
can see nothing but white sand, often drifting about on the wind, and
here and there thrown into long ridges such as those made by a
snowstorm. There are other plains, equally large, where no sand
appears, but brown barren earth utterly destitute of vegetation. There
are others, again, on which grows a stunted shrub with leaves of a pale
silvery colour. In some places it grows so thickly, interlocking its
twisted and knotty branches, that a horseman can hardly ride through
among them. This shrub is the _artemisia_--a species of wild sage or
wormwood,--and the plains upon which it grows are called by the hunters,
who cross them, the