Among these African deserts, however, there are some fertile spots. They are occasioned by springs which arise in little dells, and which saturate the ground with moisture for some distance around them. The water from these springs flows for some distance, in many cases, in a little stream, before it is finally lost and absorbed in the sands. The whole tract under the influence of this irrigation clothes itself with verdure. Trees grow up to shade it. It forms a spot whose beauty, absolutely great, is heightened by the contrast which it presents to the gloomy and desolate desert by which it is surrounded. Such a green spot in the desert is called an Oasis. They are the resort and the refuge of the traveler and the pilgrim, who seek shelter and repose upon them in their weary journeys over the trackless wilds.