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Geology of the Nahe valley

400 million years ago, in the Devonian period, Europe was near the equator and the climate was warm. A shallow ocean with islands covered central Europe, in which Hunsrück formed a deeper basin of this ocean with a stable layering of water. The upper water layers were rich in oxygen and supported life, whereas the lower levels were poor in oxygen and poisoned by hydrogen sulphide. The remains of living organisms sank into the black mud and were quickly preserved by ferrous sulphide, which is why they have kept so well. In the Herrenberg slate quarry near Bundenbach a large number of world-renowned fossils were found that, when x-rayed, showed even the finest details. The rivers that flowed into the Devonian sea deposited large amounts of muddy sediment, sand, gravel and clay, which, due to pressure and heat over millions of years, became layers of stone and rock. In this way, depending upon the material and coarseness, slate, sandstone, and (with a high percentage of quartz grains) Taunus quartzite were created.

300 million years ago, at the end of the Carboniferous period, the Devonian layers of the Hunsrück were pushed together by massive pressure from southeast to northwest creating the Variszicum mountains (the northern chain). Together with the Hochwald, Idarwald, and Soonwald chains, a high mountain range was formed. The debris resulting from the erosion and weathering of this range was deposited in the basin on the south flank, building up the "Lower Rotliegende". After another rising of the mountains and sinking of the basin the process was repeated creating the "Upper Rotliegende". During the Permian period the formation of mountains was accompanied by strong volcanic activity on the southern fault of Hunsrück. Lava welling up from inside the earth cooled and formed layers harder than the Rotliegende. Depending on the composition of the lava and the rate of cooling, very different types of rock were created: from thin lava with little silicic acid (SiO2) came basalt, melaphyre, and dolerite (Hellberg). Lava with a medium level of SiO2 created andesite and porphyre (Lemberg), and from thick lava with a high level of SiO2 came red-coloured rhyolite (Rotenfels). Occasionally gas bubbles were preserved in the lava and later filled with minerals to form agate geodes. This combination of geological formations weathering at different rates is the basis for the varied landscape of the Nahe valley, with rocky narrows where the river must force itself through and wide valley meadowlands where debris could more easily be washed away. The picture above shows the Rotenfels massif, the highest cliff wall on this side of the alps and a popular destination for climbers.

The landscape of the lower Nahe between Bad Sobernheim, Bad Kreuznach, and Bingen still essentially resembles how it was in the Oligocene period, 35 million years ago. At that time the valley was covered by an ocean, whose coastline ran along the bay of Kreuznach and the bay of Staudernheim (Bad Sobernheim) with an island archipelago in the south. It is quite exceptional in the history of the earth for the coastlines from earlier epochs to still exist. In the bay of Kreuznach one can literally touch the areas of mainland, beach, and sea bottom of the Oligocene period, even after 35 million years. In the sand pits near Bad Sobernheim you can find petrified pinecones, which have been preserved in the sandy beach ("stony peas"), or admire the sea cliff south of Bad Kreuznach from Steigerberg, an island in the Oligocene sea.

Short glossary of geological terminology.

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