 With much steeper slopes on the Italian side, many glaciers drop very sharply and some, such as the Miage Glacier and the Brenva Glacier, are very heavily covered in rock debris.The massif is itself defined by broad valleys which formed along fault lines and which have subsequently been shaped by ice during the last glacial period of the ice age.During the mid-19th century the granite of the Mont Blanc massif was an important source of stone for buildings; one hundred Italian stonemasons were brought to the Chamonix valley by Charles Albert of Sardinia for reconstructing the towns of Sallanches and Cluses, both of which had at that time just been destroyed by fires.