LANDSCAPE BORN FROM THE SEA
90 million years ago, in the Mesozoic period called the Cretaceous, the Geopark area was flooded with a shallow sea. Its bottom was gradually covered with sediments of quartz sand and gravel which over time, as a result of the weight of the overburden, turned into a solid rock called sandstone. After the retreat of the sea, the resulting sandstone plain started to be affected by external forces (water, wind, ice, living organisms) that literally modelled it into an intricate mosaic of shapes. This is where you can now see the “sculptures” of nature – rock towers, rock gates, rock clocks and honeycombs.
UNIQUE IN THE WORLD – POLZENITES
Mesozoic and especially Tertiary volcanic activity gave the landscape a new face and diversity. The capriciously meandering river Ploučnice flowing through the Geopark inspired the name of one of the oldest igneous rocks of the Czech Cretaceous Plain – polzenite – and thus went down in the history of the world geology. Polzenites flew out, under dramatic circumstances, as hot magma from deep within the Earth about 75 million years ago, and since they reached the surface quickly, they remained without major cortical impurities, providing us with a variety of information about the Earth’s mantle. Then they hardened and lay hidden under a layer of local sandstone. As a result of gradual weathering and ablation of softer sandstone, polzenite veins reached the surface. The Ralsko Geopark is thus a window into the Earth
THE SECRET OF “IRON STONE”
In many places of the Geopark, the argillaceous parts of veins of volcanic rocks were mined as iron ore. Mining took place mainly in the 17th and 18th centuries, and we still find its remnants in the countryside in the form of surface stopes (called “pinkas”) and underground tunnels (at Děvín). The mined ore, called “Toneisenstein”, i.e. argillaceous iron stone, by German miners, was then melted in blast furnaces (i.e. smelteries) to obtain iron.
LANDSCAPE AMONG CASTLES
Hard volcanic rocks resist erosion significantly better than soft sedimentary rocks (sandstone). Therefore, they determine the creation of raised landforms – monadnocks or ridges. These steep and often hardly accessible peaks became convenient places for the construction of mediaeval castles (Ralsko, Děvín, Bezděz).