Hogland Series

The Hogland Series are a series of Subjotnian sedimentary rocks exposed in the island of Gogland (Hogland), the Sommer Islands and the nearby sea bottom in the Gulf of Finland. The series encompass quartz-rich conglomerates and breccias plus some volcanic rocks of mafic composition in the form of lava flows and some more silica-rich igneous rocks including quartz-porphyry. The porphyries, which lie at the top the pile, share their origin with the rapakivi granites found nearby. An exhumed Subjotnian erosion surface is exposed on the island.