Africa; and they too, in their animal and plant life, reveal the old connection with the southern continent.[805] Sometimes man himself for his own purposes converts a peninsula into an island.  Often he constructs a canal, like that at Kiel or Corinth, to remove an isthmian obstruction to navigation; but occasionally he transforms his peninsula into an island for the sake of greater protection.  William of Rubruquis tells us that in 1253 he found the neck of the Crimea cut through by a ditch from sea to sea by the native Comanians, who had taken refuge in the peninsula from the Tartar invaders, and in this way had sought to make their asylum more secure.[806]

The reverse process in nature is quite as common.  The Shangtung Peninsula rises like a mountainous island from the sea-like level of alluvial plains about it, suggesting that remote time when the plains were not yet deposited and an arm of the Yellow Sea covered the space between Shangtung and the highlands of Shansi.[807] The deposition of silt, aided often by slight local elevation of the coast, is constantly tying continental islands to the mainland.  The Echinades Archipelago off the southwest coast of ancient Acarnania, opposite the mouth of the Achelous River, Strabo tells us, was formerly farther from shore than in his time, and was gradually being cemented to the mainland by Achelous silt.  Some islets had already been absorbed in the advancing shoreline, and the same fate awaited others.[808] Farther up this western coast of Greece, the island of Leukas has been converted into a peninsula by a sickle-shaped sandbar extending across the narrow channel.[809] Nature is working in its leisurely way to attach Sakhalin to the Siberian coast.  The strong marine current which sets southward from the Okhotsk Sea through the Strait of Tartary carries silt from the mouth of the heavy laden Amur River, and deposits it in the “narrows” of the strait between Capes Luzarev and Pogobi, building up sandbars that come dangerously near the surface in mid channel.[810] Here the water is so shallow that occasionally after long prevailing winds, the ground is left exposed and the island natives can walk over to Asia.[811] The close proximity of Sakhalin to the mainland and the ice bridge covering the strait in winter rob the island of much of its insular character and caused it to pass as a peninsula until 1852.  Yet that five-mile wide stretch of sea on its western coast determined its selection as the great penal station of the Russian Empire.  The fact that peninsular India accords in so many points of flora, fauna and even primitive ethnic stock with Madagascar and South Africa, indicates its former island nature, which has been geographically cloaked by its union with the continent of Asia.

[Sidenote:  Character of insular flora and fauna.]