OAXA'CA. See OAJACO.
OB, or OBI, the great river of western Siberia, rises in two branches, the Bia and the Katune or Katunga, both of which have their origin in the Altai mountains, within the, frontier of the Chinese dominions, about let. 49° n., and long. 90° east. These branches flowing in a n.w. direction, unite to form the Olt at the town of Biisk in lat. 52° 30' n., long. 85° east. Pursuing a winding course, with a general n.w. direction, time Oh reaches the meridian of 75° e., when it turns w.. and maintains that direction to its confluence with the Irtish, the greatest of its tributaries. It then flows n.w., n., and n.e. to its mouth in the gulf of Oh, which reaches after a course of 2,000 miles. Its chief ant ents on the right are the Tom—a swifter stream than the Oh, 400 m. in length, and nav igable for the last 280 in. from the beginning of May till July—the Tehulim, and the Ket. The principal affluent tn.: the left is the Irtish, which, rising within the frontier of the Chinese territories. traverses the Altai mountains, and after a course longer than that of the Olt itself, joins that river 250 m. below Tobolsk. The trade of the Irtish, of which' the center is Tobolsk, is important. The principal towns on the banks of the Oh are
Narim, Sargut, Berezow, and Obdorsk.—The gulf of Oh is a long inlet of the Arctic ocean, 450 m. in length by about 100 in. in breadth. At present only a few steamers ply on the great water-system of the Oh; but that system, communicating. as it does between Siberia, the Chinese territories, and European Russia, is, without doubt, destined to become a great commercial-thoroughftire. The explorations of prof. Nor denskjold,' but more especially the tentative voyages of capt. in 1974 and 1876, from Dundee through the Kara sea to the gulf of Oh, have amply proved the feasibility of this direct route. This river is very rich in fish. Below its junction with the Irtish it divides itself into several parallel streams; and in the flood season it inundates great tracts of country, and presents the appearance of a waste of waters, its desolate uniform ity broken oniy by the occasional tree-tops that rise above the surface. At Obdorsk, about 20 in. s. of the southern border of the gulf of Oh, the river freezes in the middle of October, andbitettlistup,abont the middle-of May,