The Thousand Islands – Frontenac Arch region or the Frontenac Axis is an exposed strip of Precambrian rock in Canada and the United States that links the Canadian Shield from Algonquin Park with the Adirondack Mountain region in New York, an extension of the Laurentian mountains of Québec. The Algonquin to Adirondacks region, which includes the Frontenac Axis or Arch, is a critical linkage for biodiversity and resilience, and one with important conservation potential. The axis separates the St. Lawrence Lowlands and the Great Lakes Lowlands. It has many distinctive plant and animal species. It is one of four ecoregions of the Mixedwood Plains.