THE NORTH GERMAN LOWLAND is underlain by Tertiary rocks which have been covered in Quaternary times by material deposited in part by the glacial ice sheet from the north, and in part by the rivers from the south. Only in a few places do the Tertiary rocks come to the surface. The country to the east of the Elbe may first be considered. From the shores of the Baltic Sea the land rises to the heights of the Baltic ridge, which runs from Courland to Schleswig. Upon this line of heights, due in part to a movement of Tertiary times, the edge of the ice-sheet remained for a prolonged period during its retreat from the south. The heights themselves are therefore covered with morainal debris and numberless lakes, as in East Prussia, Mecklenburg, and Schleswig, while the land inter vening between the lakes is generally well-wooded. On the northern slopes of the ridges there are considerable areas of fertile land, due in part, it is believed, to the debris brought down from the limestone rocks in the south of Scandinavia. On the southern slopes of the ridges, on the other hand, the waters of the melting ice-sheet left large deposits of sand and gravel, which have rendered considerable areas poor and infertile. Beyond the Baltic ridge lies the zone of Great Valleys, each of which in turn marks the channel by which the water escaped at each successive stage in the retreat of the ice-sheet. The valley from Thorn to Eberswalde is now occupied by the Vistula, the Netze, and part of the Oder ; further south, in the Warsaw-Berlin valley, are the Bzura, Ner, Warthe, Obra, and the Spree ; while still further south lies a third valley, in which the Bartsch and the Baruth flow for part of their way. Over all this zone the character of the soil varies greatly from one place to another. In some districts there are considerable areas of good boulder clay, which are fertile ; in others the land had to be reclaimed from bog and swamp before it could be made productive ; while elsewhere, as in Brandenburg, there are wide stretches of sand on which little cultivation is possible.
To the south of the Great Valleys lies another ridge of land, beyond which the ice-sheet did not advance. This ridge is marked by heights, rather than by hills, in the south-east of Posen, in the north of Silesia, in the Flaming, and in the Luneburg Heath. The
first of these upland regions contains great stretches of sand ; in the second there is much fertile soil ; the Flaming consists of sandy wastes, marshes, and moorland ; while in the Luneburg Heath vast expanses of sand and gravel are covered with heather. In parts of Saxony and Silesia there are widespread deposits of loess, and in the country south of Magdeburg this is also the case. Some of these deposits lie in the valley beyond the Southern Ridge, which is now occupied by the Black Elster and the DrOmling.
To the west of the Elbe the country consists in the main of dreary alternations of high moors and marsh lands. The former frequently occur in sandy districts which are underlain by an impermeable subsoil, while the latter are low-lying lands which were at one time covered by water, but are now occupied by the vegetation typical of bogs and marshes.
The great inlet of the North German Plain, which lies between the Ruhr coalfield and the Teutoburger Range, and of which Miinster is the centre, consists largely of sandstones and marls of Secondary times, frequently overlaid by alluvial soils, which are generally fertile and produce good crops of cereals. There are in places forests of oak, upon the acorns of which feed the pigs that produce the well-known Westphalian hams. Horses and cattle are also reared.
The general character of the North German Lowland as fashioned by nature has been improved in many places by the hand of man. The valleys and deltas of the Memel and the Vistula, for example, have been embanked, and considerable areas of arable and meadow land thus brought under cultivation. To the south of the Baltic Ridge, again, much of the country has been drained, as in the Oder Swamp and in the valleys of the Warthe and the Netze. A great part of the heaths has also been improved in various ways. Formerly, the practice was to burn the dry heath and to sow buck wheat in the ashes until the soil formed by them had been exhausted. The present method, the results of which are lasting, is to open up the moor, to drain it, to expose it to the air, and to manure it heavily. On the low moors the peat is first removed, and the subsoil is then mixed with sand and manured with kainit.