Springs issue, however, here and there, in several places, from the ground, and, percolating through the sands along the valley, give fertility to little dells, long and narrow, which, by the contrast that they form with the surrounding desolation, seem to the traveler to possess the verdure and beauty of Paradise.

There is a line of these oases extending along this westerly depression, and some of them are of considerable extent.

The oasis of Siweh, on which stood the far-famed temple of Jupiter Ammon, was many miles in extent, and was said to have contained in ancient times a population of eight thousand souls.

Thus, while the most easterly of the three valleys which we have named was sunk so low as to admit the ocean to flow freely into it, the most westerly was so slightly depressed that it gained only a circumscribed and limited fertility through the springs, which, in the lowest portions of it, oozed from the ground.

The third valley--the central one--remains now to be described.
The reader will observe, by referring once more to the map, that south of the great rainless region of which we are speaking, there lie groups and ranges of mountains in Abyssinia, called the Mountains of the Moon.
These mountains are near the equator, and the relation which they sustain to the surrounding seas, and to currents of wind which blow in that quarter of the world, is such, that they bring down from the atmosphere, especially in certain seasons of the year, vast and continual torrents of rain.