Such supplementary agriculture usually shifts with the nomad group. But where high mountains border rainless tracts, their piedmont districts regularly develop permanent cultivation. Here periodic rains or melting snows on the ranges fill the drainage streams, whose inundation often converts their alluvial banks into ready-made fields. The reliability of the water supply anchors here the winter villages of the nomads, which become centers of a limited agriculture, while the pasture lands beyond the irrigated strips support his flocks and herds. Where the piedmont of the Kuen Lun Mountains draws a zone of vegetation around the southern rim of the Takla Makan Desert, Mongol shepherds raise some wheat, maize and melons as an adjunct to their cattle and sheep; but their tillage is often rendered intermittent by the salinity of the irrigating streams.[1119] Along the base of the Tian Shan Mountains, the felt yurt of the Gobi nomad gives place to Turki houses with wheat and rice fields, and orchards of various fruits; so that the whole piedmont highway from Hami to Yarkand presents an alternation of desert and oasis settlement.[1120] Even the heart of arid Arabia shows fertile oases under cultivation where the lofty Nejd Plateau, with its rain-gathering peaks over five thousand feet high, varies its wide pastures with well tilled valleys abounding in grain fields and date-palm groves.[1121] Along the whole Saharan slope of the Atlas piedmont a series of parallel wadis and, farther out in the desert, a zone of artesian wells, sunk to the underground bed of hidden drainage streams from the same range, form oases which are the seat of permanent agriculture and more or less settled populations. The Saharan highlands of Tibesti, whose mountains rise to 8,300 feet, condense a little rain and permit the Tibbus to raise some grain and dates in the narrow valleys.[1122]
Irrigation and horticulture.
The few and limited spots where the desert or steppe affords water for cultivation require artificial irrigation, the importation of plants, and careful tillage, to make the limited area support even a small social group. Hence they could have been utilized by man only after he had made considerable progress in civilization.[1123] Oasis agriculture is predominantly intensive. Gardens and orchards tend to prevail over field tillage. The restricted soil and water must be forced to yield their utmost. While on the rainy or northern slope of the Atlas in Algiers and Tunis farms abound, on the Saharan piedmont are chiefly plantations of vegetables, orchards and palm groves.[1124] In Fezzan at the oasis of Ghat, Barth found kitchen gardens of considerable extent, large palm groves, but limited fields of grain, all raised by irrigation; and in the flat hollow basin forming the oasis of Murzuk, he found also fig and peach trees, vegetables, besides fields of wheat and barley cultivated with much labor.[1125] In northern Fezzan, where the mountains back of Tripoli provide a supply of water, saffron and olive trees are the staple articles of tillage. The slopes are terraced and irrigated, laid out in orchards of figs, pomegranates, almonds and grapes, while fields of wheat and barley border the lower courses of the wadis.[1126] In the "cup oases" or depressions of the Sahara, the village is always built on the slope, because the alluvial soil in the basin is too precious to be used for house sites.[1127]
Effect of diminishing water supply.
The water supply in deserts and steppes, on which permanent agriculture depends, is so scant that even a slight diminution causes the area of tillage to shrink. Here a fluctuation of snowfall or rainfall that in a moist region would be negligible, has conspicuous or even tragic results. English engineers who examined the utilization of the Afghan streams for irrigation reported that the natives had exploited their water supply to the last drop; that irrigation converted the Kabul River and the Heri-rud at certain seasons of the year into dry channels.[1128] In the Turkoman steppes it has been observed that expanding tillage, by the multiplication of irrigation canals, increased the loss of water by evaporation, and hence diminished the supply. Facts like these reveal the narrow margin between food and famine, which makes the uncertain basis of life for the steppe agriculturist. Even slight desiccation contracts the volume and shortens the course of interior drainage streams; therefore it narrows the piedmont zone of vegetation and the hem of tillage along the river banks. The previous frontier of field and garden is marked by abandoned hamlets and sand-buried cities, like those which border the dry beds of the shrunken Khotan rivers of the Tarim basin.[1129] The steppe regions in the New World as well as the Old show great numbers of these ruins. Barth found them in the northern Sahara, dating from Roman days.[1130] They occur in such numbers in the Syrian Desert, in the Sistan of Persia, in Baluchistan, the Gobi, Takla Makan Desert, Turfan and the Lop Nor basin, that they indicate a marked but irregular desiccation of central and western Asia during the historical period.[1131]
Scant diet of nomads.
If a scant water supply places sedentary agriculture in arid lands upon an insecure basis, it makes the nomad's sources of subsistence even more precarious. It keeps him persistently on low rations, while the drought that burns his pastures and dries up well and wadi brings him face to face with famine. The daily food of the Bedouin is meal cooked in sour camel's milk, to which bread and meat are added only when guests arrive. His moderation in eating is so great that one meal of a European would suffice for six Arabs.[1132] The daily food of the shepherd agriculturists on the Kuen Lun margin of the Takla Makan Desert is bread and milk; meat is indulged in only three or four times a month.[1133] The Tartars, even in their days of widest conquest, showed the same habitual frugality. "Their victuals are all things that may be eaten, for we saw some of them eat lice." The flesh of all animals dying a natural death is used as food; in summer it is sun-dried for winter use, because at that time the Tartars live exclusively on mare's milk which is then abundant. A cup or two of milk in the morning suffices till evening, when each man has a little meat. One ram serves as a meal for fifty or a hundred men. Bones are gnawed till they are burnished, "so that no whit of their food may come to naught." Genghis Khan enacted that neither blood nor entrails nor any other part of a beast which might be eaten should be thrown away.[1134] Scarcity of food among the Tibetan and Mongolian nomads is reflected in their habit of removing every particle of meat from the bone when eating.[1135] A thin decoction of hot tea, butter and flour is their staple food. Many Turkoman nomads, despite outward appearance of wealth, eat only dried fish, and get bread only once a month, while for the poor wheat is prohibited on account of its cost.[1136] The Saharan Tibbus, usually on a starvation diet, eat the skin and powdered bones of their dead animals.[1137]