 The Chazy Reef is an extensive Ordovician carbonate rock formation that extends from Tennessee to Quebec and Newfoundland.It occurs in prominent outcropping at Goodsell Ridge, Isle La Motte, the northernmost island in Lake Champlain.The oldest reefs are around "The Head" of the south end of the island; slightly younger reefs are found at the Fisk Quarry, and the youngest (the famous coral reefs) are in fields to the north.