It is the western part of the volcanic region of Rhineland
which lies before us, and in the center of which is the Laachersee or
lake of Laach. The origin of these volcanoes is not as remote as many
suppose, but their activity must have continued for a comparatively
long period, judging from the extent of their lava beds.
[Illustration: THE SHORES OF LAACHERSEE.]
There was a time when the sea covered the lowlands of North Germany,
and the waves of a deep bay washed the slopes of the Siebengebirge.
Then the bed of the Rhine lay in the highlands, which it gradually
washed away until the surface of the river was far, far below the
level of its old bed; and then the volcanoes poured forth their
streams of lava over the surrounding plains.
In the course of time the surface of the country has changed so that
these lava beds now lie on the mountain sides overhanging the valleys
of to-day. Some of the volcanoes sent forth melted stones and ashes
from their summits, and streams of lava from their sides, while the
craters of others cracked and then sank in, throwing their debris over
the neighboring country.
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