Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/192

180 that of the Sea of Aral on the other, that it can scarcely be doubted they were formerly in free communication with one other ; and the lines of this communication can be pretty certainly traced out by the peculiar lowness of the levels. Thus between the Caspian and the Black Sea, or rather the Sea of Azoff, it would have lain across the low-lying portion of the steppe, which is at present a receptacle for the drainage of the surrounding area, forming the long and shallow Lake Manytsch. And between the Caspian and the Aral Sea it probably followed both the northern and the southern borders of the list Urt, which vould have thus formed an insulated platform. If the elevation of level were sufficiently great to raise the water in Lake Aral to the height which it had in former times (as is shown by various clearly discernible landmarks), it would have overflowed a large area to the south also ; and of this again, some parts of the coast-line are traceable. A very slight further elevation would bring it into com munication with the Arctic Sea. There is much to support this view, not only in the writings of ancient geographers and in the incidental notices which have been gleaned from the records of early travel, but also in the physical relations of the three basins now forming separate seas. For if the outlet of the Bosphorus were closed, the progressive accumulation of the excess of fresh water which at present escapes from the Black Sea by that channel (see ), would in no long time cause an overflow into the basin of the Caspian ; since, although the Black Sea proper is separated from the southern portion of the Caspian by the mountainous region of the Caucasus, yet between the Sea of Azoff and the northern portion of the Caspian there is only the low steppe inhabited by the Don Cossacks and the Kalmucks ; and, according to Major Wood, an elevation of the Black Sea to no more than 23 feet above its present level would cause it to overflow into the basiu of the Caspian by the line of the Manytsch. The continuance of such an overflow would in time raise the Caspian to the same level, and would thus produce (as already shown) an immense extension of its area. For although that area would be prevented by the interposition of the Ust Urt from directly spreading towards the Sea of Aral, yet a continued rise of the Caspian would enable its water to find its way along the north and south of that plateau, so as to extend itself over a large part of the Aralo-Caspian depression, including what is now the isolated Sea of Aral, and completely surrounding the Ust Urt, which would rise as an island in the midst of it. A rise of 158 feat above the sea would bring it up to the level of the Sea of Ar.il ; and it is considered by Major Wood that a further rise of about G2 feet, making 220 feet in all, of which there is distinct evidence in horizontal water-marks, would cause this Asiatic Mediterranean to overflow its northern boundary into the watershed of the Tobol, one of the tributaries of the Obi, through which its water would be discharged into Polar Sea. And it is a fact of no little interest, that the existence of such a communication between the Aralo- Caspian basin and the Northern Ocean was most distinctly affirmed by Strabo and other ancient geographers. Now, as there is strong reason to suspect, from the evidence of recent volcanic change in that locality, that the opening of the Bosphorus took place within a period which, geologically speaking, was very recent, it does not seem at all improbable that this event (which some writers identify with the deluge of Deucalion) was the commence ment of a series of changes, by which the &quot;Asiatic Mediter ranean &quot; came to be divided into the three separate basins which now constitute its &quot; survivals.&quot; Supposing, then, the level and extent of this great inland sea to have been formerly such as just described, the effect of the opening of the Bosphorus would of course be to lower its surface and to contract its area. So long as the Caspian retained its communication with the Black Sea, it would remain at the general oceanic level, the excess of the river drainage into the western basin (including that of the Volga) supplying what was deficient in the eastern. But if, by a slight elevation of the intervening isthmus, this communication were cut off, the excess of evaporation over the Caspian area (which would have been previously separ ated from the Aral Sea) would have reduced its level all the mors rapidly, when the Volga, which now furnishes its principal supply, was not ona of its affluents ; and we can thus account for that depression of its surface much below its present level, which seems to have existed in the time uf Alexander. By the subsequent deflection of the lower part of the Volga from the Sea of Azoff into the basin of the Caspian, the level of the latter would have been raised again, and its area extended, until that equality came to be established between the evaporation-loss and the river- supply which obtains at the present time. The changes produced in the eastern portion of the &quot; Asiatic Mediterranean &quot; by the opening of the Bosphorus would have been yet more considerable. In consequence of the greater elevation of the Aruliau area, a comparatively slight reduction of level would have served to lay dry a large proportion of it, and to cut off all communication with the Caspian except by a narrow outlet ; and the mainte nance of the level in what thenceforth existed as an isolated basin would depend upon the relation between its evapora tion and its river-supply. This supply is mainly derived from two principal rivers : the Syr Darya (the ancient Jaxartes), which takes its rise in the high valleys to the east of Kokand, flows through that khanate in a westerly direction, and now, after passing Khojend, turns suddenly north wards, and then to the north-west, and finally discharges itself into the Sea of Aral near its northern extremity ; and the Amou Darya (the ancient Oxus), which rises in the plateau of Pamir and the high valleys of the Hindu Kush its sources being in close proximity to those of the Indus, and then, rapidly descending into the great Turcoman Plain, at present continues onwards in a north-west direction to Khiva, after passing which it flows into the southern end of the Aral Sea. A large proportion of the water of buth these rivers, however, is withdrawn from them in the latter part of their course, partly by percolation through the sandy soil (there being no defined river-beds), and partly through the extensive irrigation by which the dwellers along their course render productive the otherwise barren land. The supply which they bring to the existing Aral Sea does not suffice to keep it up to its present level, as is proved by recent exact observation ; and it is clear, there fore, that even the whole body of water they bring down could not have maintained the level of the far larger area over which it must have originally spread, and that this must consequently have been rapidly reduced. Now there is very distinct evidence, both historical and physical, that the Oxus, within a comparatively recent period, flowed westwards across the desert of Khwarezm, near the parallel of 39 N., and discharged itself into the Caspian basin through the Balkan Bay. And there is also much reason to believe that the Syr Darya also, or a considerable part of it, once flowed westwards where it now takes its northerly bend, crossed the desert of Kizzel Koom, and finding its way into the Uzboy furrow which skirts the southern border of the Ust Urt, poured its water into the Caspian. Thus the area now occupied by the Aral Sea, deprived of its two main affluents, must either have entirely dried up, or have been reduced to a salt marsh, until a change in their course filled its basin to somewhat above its present level.