| The message of the Rocks | |
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The territory of the Mountain Community lies in the border zone between the fertile Po Valley and the first wrinkling movements of that part of the alpine ridge which the geologists call Southern Alps. The relieves are lower than those of the real Alps, which lie more northerly; the highest elevation is represented by the “Monte Bronzone” (Bronzone Mountain-1334 metres high), which, with its geographical position and its altitude, represents a panoramic balcony on the wide plain below, whose Apennine borders lose themselves in the horizon mist. |
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Calcareous sedimentary rocks which are predominantly stratified, deposited in a marine environment between the end of the Triassic Age and the end of the Cretaceous, form the skeleton of these relieves. In the rocky layers and in the fossils which they contain, a remarkable part of the natural history of this territory, lasting about 130 millions years, can be documented. The origin of the rocks of this territory has to be looked for in the mud of a tiny marine area at the edge of the African “clod”. The depth of this sea, the Tetide, has welcomed and preserved incredible layers of debris which would become the rocks of the alpine relieves and of our mountains. |
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The flint-stone, the raw material used for the prehistoric man’s tools, can often be found in some rocks belonging to our territory and documents the period in which the Tetide used to reach its utmost depth. On the contrary, the corals and the other reef beings, which can be found as debris in the calcareous rocks, remind us of some environments of the current tropical seas, where such beings build coral reefs teeming with every kind of life. On the contrary, the message conveyed by the marly and detrital rocks, such as the “pietra serena” (serena rock) from Sarnico or the Sirone conglomerate which can be found in the hilly relieves at the edge of the plain, is different; these rocks have formed close to the shore, while big and small reptiles used to walk on the emerged regions and others used to swim across the waters or fly in the primitive atmosphere. So, the rocky layers are really “pages” on which the natural history of a territory has been written. The Sebino area relieves witness an uninterrupted sequence of geological events starting from the formation of the Tetide sea basin up to the formation of the first alpine relieves. Damaged by the erosion, these last ones have supplied the series of debris which have formed the most recent rocks of our territory, which lie at the edge of the plain. Observing the rocky walls along the lake shores, you can see that the layers are often bent. As a curled mantle, the Sebino sector of the Southern Alps catches the observer’s eye with a series of corrugations where the layers packs alternatively appear to bend high (anticline) and low (syncline). The folds are sometimes modest, as close to the walls that impend over the coast road between Punta Tufo and Portirone, but other kinds of folds also exist, so huge that to observe them you have to go to the opposite lake shore. In this way, on the lake side of the “Monte Creò” (Creò Mountain), you can admire the outline of the series of synclines constituting the area of Parzanica, which goes on with the layers of the wider syncline of Tavernola. The accentuation from the tectonic efforts has sometimes caused the lying down of the folds and the breaking of the most “stretched” side, giving rise to the shifting and overlapping movements of huge packs of layers along almost horizontal surfaces. These are the dynamics of the thrusts, which on this territory have their most eloquent examples in the “Monte Bronzone” (Bronzone Mountain) masses and in the “Vasti di Predore”. The current geography of this territory is the local result of the action of huge forces even able to bring the continents nearer to each other. The vicelike grip which has suffocated the Tetide Sea has acted more intensely during the Cainozoic Era starting from 150 millions years ago, making our territory come afloat by rising huge sedimentary heaps from the sea depths. From that time on, the outer shaping agents have acted unceasingly. |
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A geomorphologic imprint, which is today extremely visible, has to be attributed to the quaternary glacial events. Still present even ten thousand years ago, the last glacial tongue belonging to the “Valle Camonica” (Camonica Valley) has given birth to the abrasion of the rocks, to the entrainment and depositing of rough debris and of erratic boulders, in the same way as all those which have come before. The ices have dug the bottom of the lake basin and “planed” the rocky sides and for this reason the lateral valleys have remained as “hanging”; still today their waters have to find their way to the lake through some falls, as you can see at Portirone or Predore. In the places where the progressive glacial melting put an end to the running of the glacier, some glacial debris used to accumulate, by forming morainic bars. In some cases, these lengthened little hills used to block the valleys up where, by obstructing the water flow, they gave birth to transitory little lakes, which would be shortly filled with clays and then by alluvial debris. Some remains of these old water mirrors are present in the basin of Celatica-Tolari, in the towns of Credaro, Gandosso and Foresto Sparso and at the entrance of the Adrara Valley. In a discreet but effective manner, if we judge the effects extent, the karstic action has worked together with the glacial action. Our mountains are prevalently made of coal and for this particular reason their rocks have been exposed to the chemical attack of the meteoric waters. Dolinas, swallow holes and hollows are the visible and circumscribed marks of these phenomena which, even if they show themselves on the surface, keep on working also in the deeper layers by creating and widening the present caves. In a diffused and not less interesting manner than in the caves, the water has engraved the surface of the rocks, by creating a fanciful collection of grooves, sharp rocky little ridges, holes and little cups. The interest towards geology reminds us that the rock not only characterizes the landscape but has also marked the history and economy of our territory. The use of the rock deeply affects the colours and architectures of the Community town centres, giving them a distinctive appearance and a kind of suitability for human living which cannot be compared to the anonymity of some modern quarters. |
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| It’s also important to remember that starting from the XV th century the sandstones of the historical quarries of Sarnico have been useful to build the portals and flights of steps of the most prestigious palaces of the territory of Bergamo, that the grindstones from Gandosso, the so-called “molere”, used to be exported in some centres of the plain even if they were extremely far, that the stone from Credaro is still today widely used for outer walls and that in the town of Tavernola the production of cement is unceasing. | |
