|  | Due to the flysch layers and the huge quantities of clay and its grey colour, central Istria is also known as Grey Istria. Since flysch layers are waterproof, the many streams have created numerous ravines through which rainfalls are descending. An important part of that region of Istria are the valleys of rivers Mirna and Raša with their tributaries, and their form is conditioned by the composition of rocks – in areas where softer flysch layers are predominant, rivers have a wide tributaries network while in areas with harder rocks rivers have incised deep and steep canyons. Due to the flourishing fauna, this area, especially the area surrounding Pazin and Buzet, is also known as Green Istria. |