Caledon Lake and the areas adjacent to it are located on a glacial spillway, comprising a deposit of peat, muck and marl. Marl is a lime-rich mud or mudstone, often found in post-glacial lake bed sediments. Marl was a key ingredient of cement in the early twentieth century. In 1908, the Superior Portland Cement Company began extracting marl from the swamplands northwest of the lake, excavating channels 300 feet long, 150 feet wide, and 40 feet deep.
-Courtesy of Heritage Caledon