The extraordinary productiveness of the soil is to be ascribed partly to the "blessed" rivers, so-called by the natives, which intersect the oasis-countries, and partly to the quality of the soil. Of these rivers the Oxus is the most important. From its fertilizing influence upon the land it may be compared to the Nile; although, when used as drinking-water, the latter still surpasses it in its pleasantness to the taste. Next comes the Zerefshan, whose name, "Scatterer of Gold," sufficiently indicates the blessing it scatters over its shores. Nor are the smaller rivers, such as the Shehr Sebz and the tributaries of the Yaxartes, of less importance. When we finally add, that the irrigation of the fields is carried on with as much care, and much more ease, than in other parts of Western Asia, we shall cease to marvel any longer at the rich resources of the soil, however grand and important they may still appear. I have already noticed in my "Travels in Central Asia" that the irrigation is carried on--firstly, by natural canals, called _arna_, which are formed by the irregular course of the Oxus; secondly, by _yaps_, _i.e._, smaller artificial canals, by which every village and colony is surrounded and intersected. In all places of any importance there is a high official, called Mirab (prince or warden of the water), who inspects the various aqueducts, and orders them every spring to be freed from the accumulated sand. During the winter the sluice-gates of all the principal "arnas" are closed as a protection against the inundations which naturally follow the breaking up of the ice. The cleaning of the canals takes place at the beginning of April, and the great object in view is to make them constantly deeper and narrower. The sand that is taken out is heaped up on both sides of the bank, which have thus for miles the appearance of intrenchments, and with their cooling shade protect the precious water from the burning rays of the summer's sun. To the general purposes of communication, however, these intrenched ditches are very prejudicial, although of real advantage to agriculture. Hence, the more expensive kahriz--subterranean canals--in Persia, are far more advantageous, and, moreover, preserve the water purer and cooler. The yaps and arnas in Central Asia form great obstacles to the traveller. Bridges are either very bad or altogether wanting. Let the reader imagine the trouble and the dreadful loss of time incurred, when a caravan with its heavily-laden camels has to cross from ten to fifteen of such embanked canals in one day's march. How prejudicial it is to the rivers to have so much water drawn off, we see clearly in the Oxus. Formerly it flowed, no doubt, into the Caspian Sea, now its embouchure is in the Sea of Aral,[23] and this great change in its watercourse must be ascribed, if not wholly, yet in a great degree, to the evil of the many small canals.