The Ukrainian plateau group, which passes thru the Ukraine in its entire length is hemmed in on both sides by two plain regions. Without a break they accompany the extended plateau groups in the north and south, uniting finally on the left bank of the Don and the country below the Caucasus. The northern plain district accompanies the northern decline of the Ukrainian horst, concealing a tectonically disturbed substratum; the southern district accompanies the northern border of the Black Sea and parts the broken chain of plicate mountains from the plateau group of the Ukraine.
The northern plain district of the Ukraine joins directly on to the Polish lowlands, and, indirectly, to the North German lowland.
The first section of the northern plain district is called Pidlassye (Podlakhia, land on the Polish border). Its northern boundary consists of the southern limits of the White Russian Plateau; the western boundary of the flat elevations near Sidlez and Bilsk; on the south the plain borders on the spurs of the Rostoche; in the east the boundary is the Buh-Pripat divide, which is only 170 m. high. The surface of the Pidlassye is very even, only slightly undulating in places on the north and south borders. The river valleys are very broad and flat. Only the great forest (the well-known Biloveza forest lies here) and the water-courses bring variety into the monotonous country. The main stream of the Pidlassye, the Buh, as well as its tributaries have the character of genuine lowland rivers. They flow thru their over-great valleys in great turns, divide into many arms, and form innumerable old river beds. Besides these we find, in southern Pidlassye, a large number of lakes and many swamps and moors which mark the sites of former lakes.
The chalk and tertiary substratum appears only in very few places, the rest being covered everywhere by sand and loam, which include boulders and rubble of Finnic- Scandinavian origin. These are traces of the great (second)
glacial period of Northern Europe, which covered the entire region of the Pidlassye with glacial ice. The lakes are morain-lakes. The ice of the glacial period did not reach Pidlassye. At that time a broad primeval river valley formed here as an extension of the primeval Vistula river valley. In this valley the water from the melting glacier flowed off to the east toward the lowland of the Polissye. The Polissye (woodland) is one of the most remarkable lands of Eastern Europe. Only a low (170 m.) and very flat divide, which is crossed without difficulty by the Dnieper-Buh ship canal, separates the Polissye from the Pidlassye. In the north the White Russian Plateau approaches, in the south the Volhynian, in the east the Polissye extends beyond the Dnieper to the spurs of the Central Russian Plateau. The region thus bounded forms an immense flat trough, in the vertical axis of which the Pripet River flows. The bottom of this trough is very flat and lies at a height of 120 — 150 m. Only in places do we find almost imperceptible rises of ground. The substratum of the Polissye is composed of chalk marl with numerous holes made by springs (vikno=window), while in the east oligocene formations also appear. But this substratum is seen very seldom, all the rest of the Polissye being covered with diluvial sands and great swamps. The sands take in all the elevated places and form wandering or wood-covered dunes. These sandy rises of ground, together with the elevated banks of some of the rivers, afford the only sites for human abodes. All the remaining land is marshy wood, genuine forest swamps, bog or moor. The Pripet with its tributaries, the Stokhod, Stir, Hornin, Ubort, Uz (on the right) and the Pina, Yassiolda, Sluch, and Ptich (on the left), comprises the water system of the Polissye. All these rivers flow very slowly and deposit the mud which they bring from the plateau regions surrounding the Polissye along their courses. By this means