Sakhalin is separated from the mainland by the narrow and shallow Mamiya Strait or Strait of Tartary, which often freezes in winter in its narrower part, and from Hokkaid?, (Japan) by the Soya Strait or La P�rouse Strait. Sakhalin is the largest island in Russia, being 948 km (589 mi) long, and 25 to 170 km (16 to 106 mi) wide, with an area of 72,492 km2 (27,989 sq mi).
Its orography and geological structure are imperfectly known. One theory is that Sakhalin arose from the Sakhalin island arc. Nearly two-thirds of Sakhalin is mountainous. Two parallel ranges of mountains traverse it from north to south, reaching 600�1500 m (2000�5000 ft). The Western Sakhalin Mountains peak in Mount Ichara, 1,481 m (4,859 ft), while the Eastern Sakhalin Mountains's highest peak, Mount Lopatin 1,609 m (5,279 ft), is also the island's highest mountain. Tym-Poronaiskaya Valley separates the two ranges. Susuanaisky and Tonino-Anivsky ranges traverse the island in the south, while the swampy Northern-Sakhalin plain occupies most of its north.
Sakhalin coast of Sea of Okhotsk
Crystalline rocks crop out at several capes; Cretaceous lime stones, containing an abundant and specific fauna of gigantic ammonites, occur at Dui on the west coast; and Tertiary conglomerates,sandstones, marls and clays, folded by subsequent upheavals, are found in many parts of the island. The clays, which contain layers of good coal and an abundant fossil vegetation, show that during the Miocene period, Sakhalin formed part of a continent which comprised north Asia, Alaska and Japan, and enjoyed a comparatively warm climate. The Pliocene deposits contain a mollusc fauna more Arctic than that which exists at the present time, indicating that the connection between the Pacific and Arctic Oceans was probably broader than it is now.
Main rivers: The Tym, 330 km (205 mi) long and navigable by rafts and light boats for 80 km (50 mi), flows north and north-east with numerous rapids and
