een established makes it possible for the water to be distributed in an area 20 miles wide between the rivers, an area within which several villages are to be found. A few enclaves have been left uncultivated either through want of agricultural labor or because of inadequate drainage which renders the soil marshy.
An ample supply of water for irrigation, the presence of fertile loess soil, and a sufficient population are the essential conditions for the expansion of the oasis, but the limits of cultivation have been caused by other factors, notably the incursion of the drift-sand of the desert. The movement of the sand is influenced by the prevailing winds. However, Stein concludes that it is likely that the edges of the oasis presented in ancient times showed the same abrupt transition between cultivated ground and desert as can be seen at present. There is some vegetation in this desert of drift-sand. There is subsoil water relatively near the surface so that tamarisks and some scrub manage to grow between the dunes, and where floods from the rivers or canals penetrate into this zone, the beds remain covered with hardy Kumush grass for years.
To the south, the oasis is bordered by a mountain range which is in some ways more barren and forbidding than the desert. The whole region presents an aspect of rugged desolation, and extremes of heat and cold have produced the rapid disintegration of all exposed rocks. This along with the dryness of the climate accounts for the restricted plant growth in these barren mountains, where only scanty tufts of hardy scrub are to be found. In the narrow valleys, it is possible to grow oats, but not in sufficient quantities to maintain even a sparse population. There is no indication that the physical conditions in these mountains have changed in historical times. No important trade route has ever passed through these mountains. Stein has searched the historical record for references ...