Though the unfathomed mass of this alluvium* at the slowly advancing delta of a sluggish river, yet annual additions are now made to it within the area affected by the floods. The deluge from the swollen river creeps wide inland and, as it recedes, leaves its fine layer of sediment on the surface of the desert. Shells from the river are carried with the inundating waters. They are deposited with the fine silt, and left high and dry as the waters retire. The
* has been mainly deposited