But the great lakes which covered the country during the Lacustrine period have disappeared, leaving behind them immense marshes like those of the Pripet and in the N.E.
A third depression, traversed by the Pripet and the middle Dnieper, extends to the W.
Dvina, and the Pripet, both very important for navigation - as well as several smaller tributaries on which rafts are floated; on the left the Sozh, the Desna, one of the most important rivers of Russia, navigated by steamers as far as Bryansk, the Sula, the Psiol and the Vorskla.
The Dnieper and Bug canal in Grodno connects the Mukhavets, a tributary of the Bug, with the Pina in the basin of the Pripet, that is, the Dnieper with the Vistula.
The lime appears in groves only in the east (Memel, Pripet, Lublin).
Brest-Litovsk, at the western issue from the marshes of the Pripet, the towns of Dubno, Lutsk and Bobruisk constitute the second line of defence.
About the town of Smolensk the breadth is 455 ft., at the confluence of the Pripet 1400, and in some parts of the Ekaterinoslav district more than 14 m.
Of the tributaries of the Dnieper the following are navigable, - the Berezina and the Pripet from the right, and the Sozh and the Desna from the left.
Coniferous forests, consisting mostly of pine (Pinus sylvestris) and birch, cover large tracts in Mazovia in the north, extend across the Baltic lake-ridge southwards as far as the confluence of the Bug with the Narew, and join in the south-east the Polysie of the Pripet.