At the southern end of the Milbanke Sound Group, a small monogenetic cinder cone with an elevation of resides on Dufferin Island. It sent basaltic lava flows to the north where they reached the island's shoreline to cover beach gravel. Since its formation, the cinder cone has been eroded and covered by forest. Finngal Island, south of Dufferin Island, contains one or more basaltic lava flows that form well-preserved columnar jointing. Like other volcanic deposits in the Milbanke Sound Group, little is known about these lava flows.