Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/191

Rh depressed area about 79 feet below the present level of the Caspian, and more than 160 feet below that of the Black Sea. Everywhere the sand of these steppes contains an admixture of salt ; and there are various local accumula tions of salt, often associated with marl, having shells and fish-bones imbedded in them, and thus clearly marking the Bites of lakes which survived for a time the reduction of level and recession of the northern border of the Caspian, but which are now entirely dried up.

Climate of the Caspian.—The temperature of the Caspian area is remarkable for its wide range, both geographical and seasonal, the difference between the mean winter temperatures of its northern and southern extremities being very great, whilst over its whole extent a high summer temperature prevails. The January isotherm of 1 5 skirts its northern border ; that of 20 crosses it at the line of division between its northern and middle basins ; that of 30 crosses it between its middle and its southern portions ; and that of 40 skirts its southern border. Thus between the mean winter temperatures of the northern and southern extremities of the Caspian there is a geographical range of 25. These means, however, do not indicate the extremely low temperatures which prevail over the whole region of the steppes during the prevalence of north-east winds ; the thermometer then sinking to 20, or even lower, on the level areas, whilst on the elevated plateau of Ust Urt a temperature of - 30 is nothing remarkable. The July isotherm of 75, again, crosses the middle basin of the Caspian, nearly coinciding with the January isotherm of 25 ; and that of 80 skirts the southern border of the sea, nearly coinciding with the January isotherm of 40; so that the mean annual range is 50 over the northern portion of the basin, and 40 at its southern extremity. These sum mer means give no truer indication than the winter means of the extremes of temperature occasionally reached ; thus Major Wood saw the thermometer mark 110 in the shade on the bank of the Oxus, recalling to his recollection the intense heat of Annesly Bay in the Abyssinian expedition. The shallow northern basin of the Caspian is frozen during the entire winter, and the ice sometimes extends to the middle basin ; the deep southern basin on the other hand, is never frozen over. The prevalent winds of the Caspian are the south-east, which usually blow between October and March, and the north or north-west, which are common between July and September. They sometimes continue with great violence for days together, rendering navigation dangerous, and inundating the shores, wherever these are low and flat, against which they blow. The same cause tends to disturb the general level of the water, which is raised or lowered by from 4 to 8 feet at the north or the south end of the basin, according to the direction of the wind ; and when this changes suddenly, as it often does, strong currents arc generated. There are no perceptible tides in the Caspian ; and the changes of level occasionally observed without any wind to account for them seem attributable on the one hand to inequality between the evaporation and the return of water by rain and rivets, and on the other to differences in atmospheric pressure between one part of the area and another, such as alter the level of the Baltic (see ). It was stated by Colonel Monteith (Royal Geographical Journal, vol. iii.), that during his residence in that part of Asia from 1811 to 1828, the Caspian, &quot; as well as every other lake in Persia, had sensibly decreased in depth ; &quot; but according to the information given him by the inhabitants of Enzeli, there is a rise and fall of several feet in periods of thirty years ; and Von Baer, by whom the question was carefully examined, could not obtain an evidence that any continuous reduction of level is at present in progress. There is indeed reason to believe that the level of the Caspian was once much lower than it is at present ; for at Derbend, whose foundation is assigned to Alexander, masonry has been ascertained to exist at a depth of 50 feet below the present surface level ; and as it is recorded that the Khorasmians made an offer to Alexander to conduct his army to Colchis, it would seem as if the ridge at the southern end of what is now the middle basin could then have been crossed dry-shod. This does not appear very improbable, if, as ancient geographers and historians ex plicitly state, the Volga flowed in their time, not into the Caspian, but into the Sea of Azoff, a condition which seems to have persisted as late as the 5th century. The channel of its lower part would then have been that of the present River Don, which at one part approaches so closely to that of the Volga, that the two are united by a canal of less than 50 miles' length.

Fauna of the Caspian.—The animal life of this inland sea presents a remarkable admixture of marine and fresh water types. The presence of seals and herrings seems an unmistakable indication of its former communication with the ocean, and this rather northwards with the Polar Sea than westwards through the Black Sea and Mediterranean. Again, the Caspian abounds in salmon, a fish that may be considered essentially marine, though resorting to rivers to breed. And among its most notable and valuable inhabi tants are four species of Sturicnidce the sturgeon, the sterlet, the sevriouga, and the beluga which are essentially estuary fish, ascending rivers from their mouths. The fisheries are extremely valuable, a very large amount of fish being salted for transmission to distant parts, while the Sturionidse afford the principal supply of caviaro (prepared from their roe) and of isinglass (their swim- bladders cut into strips) for the whole world. The Molluscan fauna is not by any means proportionally numerous or varied. It principally consists of these wide spread marine forms which are able to adapt themselves to a variety of conditions, and especially to a reduction in the salinity of the waters they inhabit, which (as in the parallel case of the Baltic) tends to dwarf the races of mollusks subjected to it.

Naphtha and Petroleum Springs.—Various parts of the shore of the Caspian abound in naphtha and petroleum. This is especially the case with the Peninsula of Apsheron, and with the Island of Tchilehon or Naphthalia, which lies near the opposite coast, off the Bay of Balkan. The whole soil of Apsheron is said to be saturated with naphtha, which rises wherever a hole is bored ; and round the town of Baku there are nearly a hundred bituminous springs, from many of which considerable supplies of naphtha are drawn. Some of these are constantly burning; and one of them, termed the &quot; burning field,&quot; was formerly a celebrated &quot; shrine of grace &quot; to the Ghebers or Parsees, multitudes of pilgrims resorting to it, as Mahometans do to Mecca. Former Extent of the Caspian.—From what has been stated, there can be no reasonable doubt (1) that the area of the Caspian must have formerly been much more exten sive than at present, and (2) that it must at some time have had free communication with the ocean. It was long since pointed out by Pallas that the presence of salt lakes, dry saline deposits, and sea shells of the same species as those now inhabiting the Caspian, over a very large extent of the steppes to the east, north, and west of the present basin, can only be accounted for on such an hypothesis ; and he traced out what may probably be regarded as a northern shore-line, along the base of the Mongodjar hills. Further, the fauna of the Caspian corresponds so remark ably with that of the Black Sea on the one side, and with 