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Stone and man


All Tertiary volcanic rocks belong to a separate volcanic area of ​​northeastern Bohemia (Turnov-Jičín), which has its specific petrographic character, different from the Bohemian Uplands. These are mostly solid subsurface (erosion today rendering of naked volcanic chimneys, Pňov, right, and bed vein Laccoliths), only in the case of the northern side and the top of the mold surface Kozákova (sheets and flows and pyroclastic material). Chimney volcanic breccia are pierced younger genuine compact igneous veins and are then called pňovými veins. Besides Kozákovian effusion olivine basalt, which corresponds to the oldest čtvrtohorám include other volcanics to the older, ie the main stage, which falls into the lower Miocene. Specific phenomena are called Devil walls. It is characterized by geological character that is specific for this region neovulkanitu. Nefelinitové magma penetrated in some places in the form of bedding veins 3–6 meters into the powerful horizontal beams Cretaceous sediments, which were splayed, reaching deep cracks that formed the action of tangential pressure and in which said intrudovalo magma. Rock that formed the walls of the Devil, was nefelinit olivine. Mineral nepheline, which constitutes approximately 50% of the mass of rock, and it is replaced by feldspars. Along with him through the rocks occurring minerals olivine and titanomagnetit and very rarely analcime.

Traces of one of the so-called Devil's walls can be seen in the length of over one kilometer near the village burial and other places Žehrov forest. It is a relatively little-known Devil's Wall north-south direction, now almost throughout Extracted direction for building stone. Was partially uncovered in the sand pit near Žehrov and was characterized by the disintegration of horizontal columnar basalt.

GPS position

N 50° 30.831', E 15° 4.754'



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