The underlying rocks consist of northwest striking Permian (?) or older limestone, quartzite, calcareous schist, hornblende schist, and chloritic schist. Bodies of crystalline limestone are the dominant lithology outcroping along the north end of Banks Island for about 3 kilometres. These rocks are in fault contact with sheared quartz diorite on the east and a 100 metre wide contact zone with granodiorite on the west.