| Ice ages and glaciation: |
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Great areas of Germany are covered with glacial sediments.
During the last 500 000 years three, maybe more periods of glaciation occur in the northern hemisphere. Thick ice covered Scandinavia and moved slowly to the south. In Germany the southernmost glaciers reached Dresden, Erfurt and Dortmund.
The three main glaciations are named after rivers: Elster, Saale, Weichsel.
The first two are located in Thuringia, the Weichsel (now "Wisla") in Poland.
The moving glaciers formed the landscape and transported huge masses of rocks, gravel and sand. Most of these materials came from Sweden, the area of the Baltic Sea, western Finland and Norway.
All stones moved by ice are called „Geschiebe".
Some of these rocks are special. They have a special texture, rare minerals or other typical features and they occur only in one area in the north. These stones can be recognized wherever they are found. Even far away from their origin. If a rock can be assigned to a single area it is called „Leitgeschiebe".
This website is about Leitgeschiebe.
Please see one here:
This rock comes from the islands of Åland in
southwest Finland. I have found it in a gravel pit south of Hamburg, but it
is common all over here.
Rapakivis have a special texture. In the Rapakivi granites large crystals of
potassium feldspar are mantled by plagioclase. This plagioclase is often
white on weathered surfaces.
Due to their typical mineral composition the Rapakivis from Åland are easy
to recognize. In Germany, Netherlands and Poland rocks from Åland are common,
even the distance from Hamburg to their origin is nearly 1000 km in a
straight line.
In fact the distances are longer. The ice with the stones inside didn't take
the direct way and these rocks can be found far in the south. (There is an
Åland Rapakivi in the pavement in front of the Frauenkirche in Dresden.)
The knowledge about the glaciations and the transport of stones from the
north to the south is called „Geschiebekunde". This part of geology arouse
in the 19th century and is still in progress. Meanwhile approximately 300
Leitgeschiebe have been established.
In case you are interested in more, have a look at the collection. The rocks
are ordered in respect to the regions of origin and start with the South of
Sweden .
The name of the rocks are mostly taken from the places they come from.
The explanations are in German, but you will see pictures too. Most of the
rocks on this website are Leitgeschiebe.
Some rocks occur at different places in the north - that's why it is not
possible to assign them.
Collection of Scandinavian rocks.
