In more than one place the boundary of the mountains of
Central Germany resembles a coast-line rich in islands.
Even at a considerable distance heights of firm rock lift
up their bold heads out of the loose diluvial land. Most
of them fare but ill; human labour is swift to attack
them. The limestone mountains of Rüdersdorf, to the
east of Berlin, are being so quickly quarried that deep
hollows are already yawning where hills once stood.
The proud chalk cliffs of Rügen, however, still shine out
to sea, and the fretting waves still toss round the rock of
Heligoland. In other parts, the deepest borings of the
world have dived beneath the flat and uniform upper
surface into the fundamental rock, and there reached its
treasures of salt, gypsum, and coal. On the whole,
however, our knowledge of the outline and composition
of these deeper rocks is but fragmentary.

The filling up of their hollows and the levelling of
their surfaces was begun even in the Tertiary period;
partly by the seas which entered through the Moravian
gap into Upper Silesia and Galicia, and in the north
only gradually abandoned Northern Germany; partly by
deposits that took shape on the new mainland, in whose
lakes and swamps the products of a luxuriant vegetation
formed those beds of lignite which exist below the bays
of the Silesian and Saxon lowland, and on the surface
of the Mark, no less than in the Bohemian basin and
the Alpine foreland. These Tertiary formations, however,
were subjected to the destructive catastrophe of the
Glacial Period, which dislocated their strata, and buried

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