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After approx. another 70 metres, on the right, there is a clearing which is the last available parking area; after that the footpath is blocked on the left by a pole and an iron barrier, which show that vehicles cannot pass. It is therefore advisable to keep to the right (please mind the remaining part of the barrier which reaches the right hand-side of the path). A further 60 metres along the path, on the right, just after a clearing with the water system, you meet two other geological places of interest, with the relevant descriptions. The first is a millstone made of a marine sedimentary rock, called Sirone Conglomerate (Event no. 3), better known by the local name of “ceppo”, which derives from the consolidation of material eroded by weathering on land (gravel, sands and silts), carried by the rivers into the sea and deposited at modest depths, about 90 million years ago, in the Cretaceous Age. The second event is a block of Majolica (Event no. 4), a compact white limestone of deep marine sedimentary origin, dating back to 145 million to 135 million years ago, between the end of the late Jurassic and the beginning of the early Cretaceous periods, frequently arising in the southern portion of the Triangolo Lariano, which was used for the production of concrete (Cesana quarry). A little further on, on the right of the path, there is yet another place of interest, i.e. fragments of Metamorphic rocks (Event no. 5), boulders from the Valtellina and Chiavenna, transported by glaciers during the Pleistocene glacial stages and abandoned as they drew back. In the Ravella Valley you can find mica-schists and gneisses of the Alpine basement, oriented texture rocks – mainly quartz, mica and clear feldspar – and the Valmalenco serpentinites, so called because their appearance resembles snake skin (snake is “serpente” in Italian). Along the trail you can see several blocks of neatly squared serpentinite: in fact, before the Second World War, some companies “extracted” this material for building activities, cutting off these blocks almost exclusively by hand in the place where they were found, with the aid of saws and chisels.
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. Questa formazione, chiamata dai geologi Calcare di Zu, si è originata nel Triassico superiore (circa 210 milioni di anni fa), in condizioni di mare caldo, limpido e poco profondo (un habitat ideale per la vita dei coralli), simile a quello delle attuali barriere coralline nelle zone tropicali ed equatoriali. Si tratta di una roccia compatta, di colore grigiastro, soggetta ad erosione da parte delle acque meteoriche acide (carsismo). Essa costituisce il pendio orientale dei Monti Cornizzolo e di Pianezzo, nonché parte del Prasanto. Percorsi circa una ventina di metri, il fondo da asfaltato diventa acciottolato e si prende a costeggiare il torrente Ravella. Dopo altri 100 metri, sulla sinistra, è stato posto un pannello che illustra la geologia dei Corni di Canzo, una delle aree geologicamente più complesse delle Prealpi. Circa 50 metri più avanti, sempre sulla sinistra, un altro pannello illustra il fenomeno dello “Slumping” (Evento n. 2), che interessa la formazione sedimentaria affiorante al bordo del sentiero, detta Calcare di Moltrasio (la più diffusa nel Triangolo Lariano, risalente al Giurassico inferiore, circa 190 milioni di anni fa), che qui presenta una stratificazione a pieghe, dovuta allo scivolamento e piegamento dei sedimenti in via di consolidamento su un pendio sottomarino, a profondità abbastanza elevate.
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