The sub-Carpathian hill country reaches to the two sub-Carpathian plains in the north—the Vistula and the Dniester Plain. Only along the European main divide a tongue of hill-country projects in the direction of Lemberg. In the glacial period, watercourses of great volume flowed directly across this hill-country divide, which, as might be expected, is now completely cleft by the bifurcation of the Vishnia, depositing considerable masses of rubble-stone and sand. Thru destruction of forests, the sands have become subject to wind action and dreary landscapes of sand-dunes have been formed. Only the southeastern reaches of the Vistula Plain, extending along the San River to Peremishl are part of Ukrainian territory. The low loam bags, which lie between sandy and swampy valleys of the San, form the only rises of ground in this plain, which borders in the northeast on the spurs of the Rostoch. The Dniester Plain extends in a broad ribbon along the river from the place where it leaves the mountains to the delta of the Striy. Its western part is a single great swamp region, a one-time large lake. The rivers flow on flat dams, and when the melting snows come and the rains of early summer, they overflow their banks and flood the swampy plains far and near. In some years the swamp region changes into a lake for days and weeks. In the dry season only a few swamp lakes remain, but the entire region remains a swamp and produces only a poor sour hay. Settlements lie only on the high banks of the rivers. [34] The eastern part of the Dniester Plain extends beyond the great alluvial mounds of the Striy River, and then reaches over into the broad valley of the Dniester, which ends in the Podolian Plateau at the point where the river enters. The eastern Dniester Plain is not very swampy, and only in places do ravines, swamps, and old river beds accompany the river course. For the most part pretty meadows, fields and woods lie on the thick sub-layer of rubble-stone and river-loam. If the Carpathians represent a primeval section of Ukrainian ground, the mountain ranges of Crimea and the Caucasus were entirely strange to the Ukrainians not so very long ago. How many Ukrainian slaves, in the time of Tartar oppression, cursed the rocky-wall of the Yaila which separated them from their beloved home. How discontented was the enslaved remainder of the Zaporogs when transported to the Western Caucasus. Now the conditions are quite changed. The great colonizing movement of the Ukrainians touched the Yaila as much as twenty years ago, and has extended the frontiers of the Ukrainian settlements along the outer mountains of the Caucasus to the Caspian Sea. And the once strange, hostile mountain-worlds have opened their doors to Ukrainian colonization.