Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/815

Rh little covefj; but excepting the Sakaria (tlie ancient San- garius), there is no considerable, river, and the water deepens very rapidly to 20 fathoms or more. Although it is known that the depth of the central part of the basin of the Euxine reaches 1070 fathoms, the ex tent of this deep depression is not known. The increase of depth off the low-lying western and north-western shores is very gradual and regular, the lines of 20, 30, and 60 fathoms maintaining a general parallelism to the coast, so that within this range the distance of a ship from land can be approximately ascertained by sounding. But out side the 60 fathom line the bottom deepens more rapidly and less regularly, depths of from 600 to 700 fathoms being met with in some pirts within a few miles of it. The depth of the eastern portion of the basin has not been ascertained, but it is probably considerable. The basin of the Euxine communicates with that of the Sea of Marmora by the Bosphorus, a strait about 20 miles long, from f to 2- miles wide, and a depth of from 30 to 40 fathoms, resembling a broad river with high banks, which maintain a general parallelism, although the strait has seven distinct reaches. The region on either side presents distinct evidence of recent volcanic action. The Sea of Marmora lies in the course of the channel that connects the Black Sea with the ^Egean. Its bottom is depressed to a depth far greater than that of the chan nel of which it is an expansion. Its length from strait to strait is 110 geographical miles, and its greatest breadth is 43 miles. Hound the shores, the depth gene rally ranges from 10 to 30 fathoms ; but it rapidly increases in most parts; and depths of 100, 133, 266, and even 355 fathoms have been met with, chiefly near the line connecting the two straits. The channel which connects the Sea of Marmora with the ^Egean is properly termed the Hellespont, the name Dardanelles, by which it is commonly known, being really that of the fortifications erected en the two sides of the strait by which its passage is guarded. The Sea of Marmora narrows to a breadth of ten miles towards the north-eastern entrance of the channel ; at Gallipoli, the distance between the two shores suddenly contracts to about two miles ; and between this and the yEgean end of the strait, that distance is further diminished at certain points to even less than a mile. The depth of the channel is considerable, being for the most part between 30 and 50 fathoms.

Climate.—The climate of the Black Sea is very peculiar, the range of temperature between the summer and winter extremes being remarkably great. The summer isotherm of 70 runs a little way inland, nearly parallel to its north western coast-line, whilst the summer isotherm of 80 passes along its southern coast-line, which is as warm as the southern coast-line of the Mediterranean, nearly 10 nearer the equator. Thus the whole area of the Black Sea lies, like that of the Mediterranean, between these two summer isotherms ; and the evaporation from its surface during the warmer part of the year will consequently be enormous. During the winter months, on the other hand, the Black Sea is exposed to the chilling winds which come down to it from the Arctic regions, sweeping over the snow-covered plains of Russia, without any interruption from high mountain ranges ; and nearly the whole of its area lies between the winter isotherms of 30 and 40, the former passing round its northern coast, while the latter passes from the Bosphorus to Poti in Mingrelia. Thus it happens that, notwithstanding their high summer tempera ture, the northern shores of the Black Sea are more or less blockaded with ice during the winter, -this being most the case where the water is shallowest, and has its salinity lowered by the entrance of rivers. Thus the Sea of Azoff and the Strait of Yenekale are always frozen over, as are also the northern ports between the Crimea and Odessa ; while, on the other hand, the harbours of Kafi a and Sebas- topol are never closed, and that of Odessa but seldom. It is recorded, however, that in 401 A.D. the surface of the Euxine was almost entirely frozen over, and that when the ice broke up enormous masses were seen floating in the Sea of Marmora for thirty days. In 762 A. D., again, the sea is said to have been frozen from the terminal cliffs of the Caucasus to the mouths of the Dniester, Dnieper, and Danube ; and contemporary writers assert that the quan tity of snow which fell on the ice rose to the height of from 30 to 40 feet, completely hiding the contour of the shores, and that on the breaking up of the ice in the month of February, the masses of it carried by the current into the Sea of Marmora reunited in one immense sheet across the Hellespont between Sestos and Abydos. No similar occurrence has been subsequently recorded. The ivinds of the Black Sea are variable, except during summer, when they generally blow from the north-east, while at other seasons southerly or south-westerly winds often prevail. The area is very subject to fogs, which appear to proceed from the precipitation by a cold northerly current of the moisture which has been raised by evapora tion from its surface, or has been brought thither by S. or S.W. winds. This sea is remarkable for the rapidity with which violent storms not unfrequently arise, often to sub side again with like rapidity.

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The greater part of the drainage area of the Black Sea, like that of the Baltic, is covered with snow during the winter months, and comparatively little water is then brought down by the rivers. With the return of spring, however, the melting of the snow increases the volume of fresh water poured into the sea, its rivers being at their highest in early summer. By far the larger part of this water is discharged at its north-western border ; and the elevation of level thus produced establishes a current that sets along its western shore towards the outlet of the Bospihorus. But as the narrowness of this channel does 