These green spots in the great deserts are the counterparts of Islands
in the oceans.
If not thrown up and fed by water upheaval, how are they produced?
Are they volcanic? The Oasis of Ammonium, or Siwah, six miles long
and eight wide, contains the ruins of the famous temple and oracle of
Ammon, visited by Alexander the Great, and celebrated for the fountain
of the Sun, whose waters are warm at morning and evening, and cold at
noon.
There are several oases not long distances west of the Nile in the
Great Desert. The ancients considered them as Islands in a Sea of Sand,
but they are really elevated lakes, although not manifesting themselves
much at the surface, but underlying so closely as to render the climate
too unhealthy to live in during the summer and autumn, being of a
swampy character, and yet very productive in winter and spring. Where
do these waters soak in to produce such spots in the deserts?