Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/190

178 the southern basin, which, at the height of from 65 to 80 feet above the present level, have been furrowed out into tooth-shaped points and needles ; and if the water were again to rise to that level, it would overflow many hundred thousand square miles of the southern steppes, extending the area of the basin as far as Saratov. Now supposing the Caspian to have been formerly in communication with the general oceanic area (which will be hereafter shown to be almost a certainty), a reduction of its level and a contraction of its area would follow as a necessary consequence, whenever that communication was cut off. For, as the evaporation-area would have then been much greater than it is at present, whilst the drainage-area would have been the same, there must have been a great excess of loss by evaporation over the water returned by rain and rivers ; and this excess, pro ducing a reduction of level, would have reduced the area of the northern shallow portion, until it contracted itself within its present limits. That this reduction was rapid, is indicated by two sets of facts ; first, the absence of any erosion of rocks between the level of the old erosion and the present level ; and second, the fan-like arrangement of the limans and intervening buyors on the north-west shore, which makes it difficult to suppose that these channels can have been formed except by the furrowing of the soft soil during the sinking of the water, corresponding to that which is seen on a small scale on the muddy banks of a reservoir in which the water is being rapidly lowered by the opening of a sluice-gate.

Salinity of the Water of the Caspian.—It might have been anticipated that such a reduction in the volume of the Caspian water as must have taken place in this lower ing of its level, would have shown itself (as in the Dead Sea) in an increase of its salinity ; whereas the fact is that the proportion of salt in the water of the Caspian, though varying in different parts of the basin, and also at different seasons, is generally much less than the proportion in oceanic and even in Black Sea water. In the northern portion, whose shallowness causes the enormous amount of fresh water brought down by the Volga, the Ural, and the Terek to exert the greatest diluting influence, the salinity is so slight (especially when the ordinary volume of these rivers is augmented by the melt ing of the snows) that the water is drinkable, its specific gravity not being higher than 1O016. In the central and southern basins, on the other hand, which contain a body of salt water too large to be thus affected, the salinity is stated by Von Baer to be about one-third that of ordinary sea-water, the average sp. gr. being about 1 009. This re duction from what may be presumed to have been its original amount seems fully explained by Von Baer, who traces it to the number of shallow lagoons with which the basin is surrounded, every one of them being a sort of natural salt-pan for the evaporation of the water and the deposit of its saline matter in the solid form. The process may be well studied in the neighbourhood of Novo Petrovsk, where what was formerly a bay is now divided into a large number of basins presenting every degree of saline con centration. One of these still occasionally receives water from the sea, and has deposited on its banks only a thin layer of salt ; a second, likewise full of water, has its bottom covered by a thick crust of rose-coloured crystals like a pavement of marble ; a third exhibits a compact mass of salt, on which are pools of water whose surface is more than a yard below the level of the sea ; and a fourth has lost all its water by evaporation, the stratum of salt left behind being now covered with sand. A similar concentration is taking place in the Karasu ; for notwith standing the proximity of the mouths of the Ural and Volga, the proportion of salt there rises to such a degree (the sp. gr. being 1 057) that animal life is almost, if not entirely, suppressed. In the Peninsula of Apsheron, again, there are ten salt lakes, from one of which 10,000 tons of salt are annually obtained. This process of elimination goes on, however, upon its greatest scale in the Karaboghaz, whose nearly circular shallow basin, about 90 miles across, is almost entirely cut off from the Caspian by a long narrow spit of land, communicating with it by a channel which is not more than about 150 yards broad and 5 feet deep. Through this channel a current is stated by Von Baer to be continually running inwards (during the summer months, at least) at an average rate of three miles per hour ; this rate being accelerated by westerly and retarded by easterly winds, but never flowing at less than a mile and a half per hour. The navigators of the Caspian, and the Turkoman nomads who wander on its shores, struck with the constant and unswerving course of this current, have supposed that its waters pass down into a subterranean abyss, through which they reach either the Persian Gulf or the Black Sea, an hypothesis for which there is not the least foundation, and which is directly negatived by comparison of levels. The current is really due to the indraught produced by the excess of evaporation from the surface of the basin, which is exposed to every wind and to intense summer heat, and which receives very little return from streams. The small depth of the bar seems to prevent the return of a counter-current of highly saline water, such as, in the Strait of Gibraltar, keeps down the salinity ef the Mediter ranean (see ), none such having been detected by the careful investigations of Von Baer. And thus there is a progressively increasing concentration of the contents of the basin of the Karaboghaz, so that seals which used to frequent it are no longer found there, and its borders are entirely destitute of vegetation. Layers of salt are being deposited on the mud at the bottom ; and the sounding-line, when scarcely out of the water, is covered with saline crystals. Taking the lowest estimates of the salinity of the Caspian water, of the width and depth of the channel, and of the speed of the current, Von Baer has shown that the Karaboghaz daily withdraws from the Caspian the enormous quantity of 350,090 tons of salt. Now, if such an elevation of the bar were to take place as should cut off the basin of the Karaboghaz from that of the Caspian, the former would quickly diminish in ex tent, and the concentration of its waters would cause an increased deposit of salt to take place on its bottom. According to the proportion between the evaporation from the area so reduced and the return of fresh water by rain and streams, the Karaboghaz would either be converted into a shallow lake of extremely salt water, or into a salt marsh, or might altogether dry up and disappear, leaving behind it a thick bed of &quot; rock-salt &quot; resembling the deposits contained in the Saliferous strata of various geological periods. These several conditions all obtain at the present time in different parts of the great area of the steppes of Southern Russia. There are several small salt lakes which receive water enough from rain, snow, and streams to compensate for the loss they sustain by evapora tion ; these especially occur in the Kirghiz steppes, which lie to the north-east of Astrakhan, between the Volga and the Mongodjar Hills that form the southern extremity of the Ural range ; the most notable of them being Lake Elton, which lies about 200 miles to the north of the present border of the Caspian, and from which large quantities of salt are annually procured. There are large tracts of these steppes, again, which are alternately muddy and white with salt, according as they are moistened by rain or dried up by the heat of the sun ; one of these, lying between Lake Elton and the River Ural, occupies a 