 Most of the islands in Georgian Bay are made of granitic bedrock, whereas the Limestone Islands are made, as their name reflects, completely of limestone.The South Island has a flat terrain inhabited by low vegetation, which is reportedly much more friendly that its sister island, the North Limestone, which is infested with poison ivy.South Limestone Island is known for being host to thousands of birds, the majority of which consist of seagulls and common terns, although there have been several unconfirmed reports of something larger living on the island, possibly an erratic albatross.