From the basalt - and its pyroclastites - found in great amounts on the ocean floor, green shale is forming during metamorphosis. In the Alpokalja region, this rock is exposed in huge quarries such as the ones at Bozsok and Felsőcsatár. The metamorphic rocks of the Felsőcsatár shale quarry belong to the shale series of Kőszeg-Rohonc. Green slate is a high-strength rock, which the Romans used to build the Savaria canal system and stone buildings, but has been abandoned since the late 20th century.