300 PIIYSIOGRAPHY OI∎ CENTRAL-ASIAN DESERTS AND OASES.
adobe roof. When the roof falls a house is abandoned or rebuilt, but most of the old débris is graded over and new material brought in for the new structure.
Fixing our eyes on Bokhara, perhaps the best example of a walled city of ancient style, we see long, heavy-laden caravans, some of camels, others of donkeys and horses, filing slowly into its crowded gates. • Other caravans are issuing, and as many as go in, from day to day; but with this difference—though most of the camels come out laden anew, some of them issue bare. And so it is with the horses, and especially with the donkeys. Whole swarms of donkeys enter loaded with mud and wood or food, and then issue with nothing. No less significant are the dust-clouded flocks of sheep and goats driven slowly into the arched gates, for but few of them ever come out again. Within the city, houses are building of the mud, and some of the wood is entering their construction, as steel does with our concrete; while some of it is used in manufactures, and the rest for firewood. Of all the food, practically none comes out; almost all ultimately finds its way to refuse piles and holes. And of articles of merchandise, all that is used therein remains as a surplus of income over outflow of that class, and becomes a
Fig. 468.—Construction of a House in the Hissar Valley.
deposition of rubbish. As long as the city lives, there is an inflowing supply of food for its occupants, and raw material to replenish the decay of their houses and supply their useful arts. The deposition of that inflow is spread more or less evenly throughout the city or whole walled area and must in time result in an appreciable growth. That such a growth does and did result is evidenced by plateaus of stratified débris that rise from out the plains where ancient cities were. From exposures in gullies and trenches, we have found that these are composed of horizontal layers of clay with pottery, bones, and charcoal, and here and there the basal remnant of a wall with part of an old floor.
Seen far out on the desert plains, where they most abound, these plateaus are unmistakable. And any one who has thought about topography can not fail to recognize them, even though the land be one of high relief. Even when much modified by erosion, as are the older ones, they still rise as contradictions to surrounding forms until obliterated by weathering or burial. It can not, however, be assumed that all artificial mounds are records of slow growth from occupation, even though left by man, for in the past he heaped mounds over the dead
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