Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/651

GEOLOGY.] PERSIA 621 cause for believing the lakes of Shiraz and Kazrun to be fed mainly by springs. St John writes further : "It will be readily believed that the rainfall on the Oceanic and Caspian watersheds is far in excess of that on the interior. Wherever the water-parting is formed, as it is in most parts, by a lofty moun tain ridge, it intercepts the moisture-bearing clouds from the sea which are discharged from its outer slopes. The Alburz chain, which shuts off the plateau from the Caspian, may be taken as the typical instance of this. Its northern face is furrowed into deep valleys by the constant and heavy showers which have clothed them in forests of almost tropical luxuriance, while the southern generally presents a single abrupt scarp, rising above long gravel slopes, unchannelled by anything worthy the name of a river, and bare of any vegetation rising to the dignity of a tree. At the most moderate estimate the rainfall of Gilan and Mazandaran may be taken as five times that of the adjoining districts across the ridges to the south. "In other parts, however, we find the water-parting consider ably below the level of the summits farther inland ; and here the interior has a more plenteous rainfall than the coast. This is par ticularly the case in south-eastern Persia, where the Khurasan, Sarhad, and Dizak hills, far exceeding in altitude the ranges to the south, attract to themselves the major portion of the scanty supply of moisture borne inland from the sea. Again the rainfall differs very much in different parts of the country, under apparently similar conditions as regards mountains and distance from the sea ; the east and south being far drier than the north and west, while the dampest parts of the Tigris valley have not half the rainfall of the southern and south-eastern shores of the Caspian. "Two palpable causes unite to produce the prevailing winds throughout Persia and the Persian Gulf. These are, with an extraor dinary uniformity, north-west or south-east. The first cause is the position of the Black Sea and Mediterranean on the north-west, and of the Arabian Sea on the south-east. The second is the bear ing of the axes of the great mountain chains, which lie mainly in the same direction, and thus tend to guide the currents of air in a uniform course. The south-west, moreover, is not felt, except as moderating the temperature of the Makran coast inside a line from Ras-al-Hadd, south of Maskat, to Karachi. "The effect of the sun on the great Iranian plateau is to produce a heated stratum of air, which, when it rises, is succeeded by a current from the colder atmospheres above the seas to the south east or north-west. Naturally the latter is the colder, and there fore, as might be expected, north-west winds are most prevalent. But in southern Persia and the gulf it often occurs that the two currents meet, and that a north-westerly gale is raging at Bushahr while a south-easter is blowing at Bandar- Abbas. This latter wind is the rain-bearer throughout the greater part of Persia, the excep tion being the north-west, where occasional rain-clouds from the Black Sea and the Caspian find their way across the Kurdish mountains or the Alburz. It is true that it often rains even on the gulf during a north-wester, but only when this has followed a succession of south-easterly gales, the moisture borne by which is returned from the opposite quarter." There are no sufficient statistics available accurately to estimate the rainfall in Persia, but St John, himself a resident of some years in the country, was of opinion that in no part of it excepting the watersheds of the Caspian and Persian Gulf (north of 28 lat.) and their immediate reverse slopes, with perhaps the Urmiya basin, is there an average of 10 inches, taking mountain and hill together. He believed that throughout the greater part of central and south-eastern Persia and Baluchistan the annual rain fall could not be much more than five inches, and that, were it not for the snow stored on the lofty hills, nine- tenths of the country would be the arid desert which one- half was found to be when he wrote (1876). Cultivation is carried on mainly by artificial irrigation, the most approved arrangement being an underground tunnel called "kanat," whereby wells are connected and supplies of water ensured. One remarkable feature in the plains of Persia which naturally engaged St John s attention was the salt-swamp called "kavir." He applied the term to those bogs of slimy mud found in the lowest depressions of the alluvial soil, where the supply of water, though constant, was insufficient to form a lake. In winter they are covered with brine, and in summer with a thick crust of salt. The principal kavir is that in Khurdsan, and marked in the maps as the Great Salt Desert. St John describes it as " the eastern part of what is probably the most extensive plain in Persia, that intercepted between the Alburz and its parallel ridges on the one hand and the heads of the ranges of the central plateau which run south east on the other. Westward, it is divided into two valleys, originating, one in the Sultdniah plateau, and the other north of and near Hamadan. These are drained by rivers named respectively the Sliurab and the Kara Sii, which, with another considerable affluent from Turshiz, on the east, unite to form the great Jcavir." He was unable to determine the altitude of this extensive swamp further than that it might be below the level of the sea, but could not be much above it. Other kavirs he finds in the Sarjan or Sayidabad plain west of Karman and in the neighbouring valley of Kutni. Among ordinary kavirs, which are "innumerable," he con siders the largest to be on the south of Khaf, and the best known that north of Kum. It is clear, from the description given, that the range of these particular salt-swamps or kavirs is confined to the actual depres sion which has been directly affected by the passage of water, and that the term is not intended to apply to the surrounding wastes. But it seems to have been otherwise understood by the generality of travellers, and the better-known writers on Persia have seldom made the actual distinction here implied. Malcolm in 1800 crossed a "salt-desert" between Pul-i-Dallak and Hauz-i-Sultan, which, he says, was called Dariya-i-Kabir, or "the great sea." Morier, nine years later, calls the place the " swamp of kaveer, . . . part of the great desert which reaches unto Khurasan, the soil of which is composed of a mixture (at least equal) of salt and earth." Colonel Johnson, passing over precisely the same road in 1817, describes it as leading "over a saline plain, leaving here and there hollows of considerable magnitude, white with salt ; . . . eastward it stretches as far as the eye can see, and is said to reach to Mausila, distant 40 miles." The writer would probably have been surprised to learn that it extended for at least ten times the distance named. He does not, however, use the word "kavir," which, while duly recorded as a Persian word in the dictionary, meaning salsuginous ground, is strangely like the Arabic adjective "kabir," which Malcolm, as just mentioned, has coupled with "dariya" in his Sketches of Persia. St John states that in the south the salt- swamps are called "kafeh." The last writer asserts that but one European, Dr Biihse, a Russian, had seen the true kavir, having crossed it in about 34 lat., when going from Damghan to Yazd. Sir Charles Macgregor must have been close upon this traveller s track in 1875, for in the district of Biabanak (the " little desert "), which he visited, one of the eight villages, Jandak, is marked in St John s map as an oasis just above the parallel mentioned. Biabanak is, according to Macgregor, situ ated "south of the kaveer," but it is joined to Semnan (on the Tehran-Mashhad highway) by a "regular road" which "crosses a bit of kaveer of about 80 miles without water." The drier deserts of Karman and Bampur cannot be included in the category of swamps ; and the term " lut," made use of by the Russian geographer Khanikoff in reference to the former, whatever its original derivation, must simply be accepted as the common local expression, in eastern Persia and western Baluchistan, for a waste waterless tract. Geology. Mr W. T. Blanford has given us an interest- Geology, ing sketch of the geology of Persia. He found that by far the greater number of those who had treated the same subject before him had restricted their inquiries to the north-western provinces, and that few had penetrated east of Dam&vand or south of Tehran. Mr Lof tus had imparted a fair knowledge of western Persia, and Russian and German explorers had made students tolerably acquainted with Adarbaijan, Gilan, and Mazandaran. Khurasan and eastern Persia generally were, however, in a geological sense unknown, and the south was almost equally a terra incognita, unless exception were made for certain stray observations on the shores of the Persian Gulf. The fol lowing passages are extracted from his paper. "The most striking circumstance noticed during a journey in Persia is the great prevalence of formations, such as gravel, sand, and clay, of apparently recent origin ; the whole of the great plains, covering at least one-half the surface of the country, consist either