UKRAINE, a socialist soviet republic of European Russia, recognised by the Soviet government in December 1920, when a treaty was signed defining the relations between the Ukraine and the Union of Socialist Soviet Republics. Area 451,730 sq.km. Pop. c. 31,901,400. It lies between 46° and 20' N. and 26° and 40° 14' E. and is bordered on the south by the Black Sea, the Crimean A.S.S.R. and the Sea of Azov, on the west by Bessarabia, on the north by the White Russian S.S.R. and the province of Bryansk and on the north-east and east by the provinces of Kursk and Voronezh and by the North Caucasian Area. The Moldavian A.S.S.R. (q.v.) is linked administratively with the Ukraine.
Geologically and structurally the Ukraine is distinct from Rus sia to the north of it; the Tertiary sea covered most of it, but extended very little further to the north, and the ice of the glacial epoch hardly reached it, except in the north-west and where Don and Dnieper mark southward extensions of glacial river sys tems. Its plateau system, the Azov Horst of Suess, composed of granite gneisses, stretches north-westwards from the Sea of Azov through Volhynia and Podolia, and is generally supposed to be the eastward continuation of the Hercynian system. This horst exerted a strong tectonic effect on the fold system of the Donetz which was thrown up from the end of the palaeozoic to the be ginning of the Tertiary period, and also caused the tectonic dis turbances of the post-Cretaceous period indicated by the lines of Karpinsky, a northern line stretching from the Volga through the bend of the Don, the source of the Donetz, the delta of the Desna and Polyesie to Warsaw and a southern from the delta of the Don, past the falls of the Dnieper to the source of the Bug. Recent seismic observations indicate that tectonic disturbances are still going on in the district and there is some evidence that elevation of the plateau region has occurred in post-glacial times.
limit of this zone and its rise may be connected with the lesser density of the forest on the loess to the south of it. Spurs of the central Russian plateau are thrust into the north-west.
But the main feature of the Ukraine is its steppe land, cov ered with chernozyom (black earth) formed on loess, more sandy to the north and more clayey to the south. The rich black earth belt runs generally south-west to north-east, diminishing in humus content towards the north and towards the south. In the south east, in accordance with more arid conditions, it displays a ten dency to salt efflorescences. Along the north shores of the Black Sea extends the Pontic steppe. The Black Sea was part of an Upper Miocene and Sarmatian Sea, which formerly extended inland as far as the Vienna basin, but which shrank in Tertiary times ; the Pontic steppe bears traces of this transgression. It approaches the sea by a steep incline only broken by the river estuaries, characterised in this region by limans. These are sub merged, eroded river valleys locked from the sea by detritus.
Where a stream of great volume enters the sea (e.g., Dniester, Bug, Dnieper), the bar is pierced in one or two places and some thing resembling a delta is formed. But in the case of those streams which do not bring down enough water to cover the loss from evaporation in the liman, the bar becomes continuous and the water within the liman is increasingly rich in salts. The mud of these limans has curative properties and small health resorts are dotted along their shores. Along the river valleys are thickets of sedge and reed, with marsh forest and meadow. The Pliocene lime which predominates in the Pontic steppe covers the crystal line substratum, which is, however, often laid bare by the action of streams. Forest destruction at the source of the streams has led to flooding after each melting of the snows. The heavy mantle of black earth and loess, the loose chalk and the marl, sand and clay of the Tertiary strata on the Ukrainian steppe are readily cut into by running water, and many acres of fertile agricultural soil have been washed away from the ravine slopes. An institute for research into amelioration of this problem now exists and efforts are being made to prevent further forest cutting, to encour age replanting and to introduce transverse ploughing across the slopes and drainage channels round the fields.