BLACK SEA BLACK SILVER 683 parts are remarkably free from rocks, sand banks, or shallows, and ships may always lie to or ride at anchor with very little danger. There is but one island in the whole sea, Serpent isle, 30 m. from the mouth of the Danube, once a sacred place, with a temple, but unoccupied for centuries, till of late years it was made a sta- tion for English and French vessels. There is now a lighthouse upon it. The principal pen- insulas are on the north, among them the Cri- mea. The depth of the sea increases regularly according to the distance from the shore ; and in its central parts no bottom is reached even by a line of 160 fathoms. There is no observa- ble ebb and flow of its waters, but its large ac- cessions from the rivers occasion strong cur- rents, which all set, with more or less direct- ness, toward the Bosporus. When these cur- rents are also helped by the winds, the waters are sent through the straits with such violence that vessels are sometimes detained for months outside, unable to enter against them. An Eng- lish surveying ship recently confirmed the con- clusion of Prof. Carpenter that these currents are only superficial, and discovered at the depth of 20 fathoms an undercurrent running with prodigious force into the Black Sea. To test the strength of this undercurrent, a special ap- paratus was constructed and attached to the ship's boats, when the boats were in many places driving along against the upper current with greater velocity than that of the steam launch of the ship. Its climate has wide ex- tremes, but is generally colder than would be inferred from its latitude, owing to the prev- alence of north winds. Its fisheries are un- Opening of the Black Sea from the Bosporus. important. The specific gravity of its water is 1-142. It contains less salt than the ocean, and freezes easily. Odessa is the most im- portant commercial port on its coast, and Var- na is the chief Turkish fortress ; besides which, the principal harbors are Sebastopol, Sinope, and Trebizond, and on the estuaries of the Bog and Dnieper, respectively, Nikolayev and Kher- son. The shores of the Black sea are known both in fable and history. Colchis, the goal of the Argonautic expedition, was on its east ; the Cimmerian region was upon its north ; and on all its sides the Persian, Byzantine, Turkish, and Russian powers have acted the events of their history. From the time of Constantine till the 15th century it was the centre of the transplanted Roman world ; and till the Cape of Good Hope was discovered and sailed round, it was a passageway of the Genoese and other European trade with the Indies. The Turks for a time excluded the ships of all other na- tions from it, and at one time Russia sought to make it a closed sea under its own mili- tary command ; but since the peace of Paris, which terminated the Crimean war, it has been open to the commerce of all nations, and the equal exclusion of all ships of war estab- lished by the neutrality clause of that treaty was abrogated at the close of 1870. BLACK. SILVER (called also brittle silver or glance, and stephanite from the Archduke Stephan, mining director of Austria), an ore composed of sulphur 16'2, antimony 15'3, sil- ver 68'5. It occurs in veins with other silver ores at Freiberg in Saxony, at Andreasberg in the Hartz, and at Zacatecas in Mexico. It is also an abundant silver ore in the Comstock lode in Nevada, and occurs in Idaho and in the Reese river and Humboldt mines. Crystals of it have been found altered to pure silver.
