Limestone and shale both contain carbon. Formation of these rocks has been removing CO2 from the atmosphere for half a billion years today. Coral and shellfish continue to do so today. Shale often contains carbon as oil and natural gas.
At Site 6 you can see Georgian Bay shale being eroded by the Humber river.
Sand, gravel, clay, and shale have been removed from the valley to build Toronto, making the valley wider and flatter that was the case two hundred years ago. At the cemetery chapel, examine the stone used in the building walls. Site 9
Lake Iroquois was a large lake formed by the melting glaciers, draining via the Hudson river. When the St Lawrence valley became ice free, the water level was reduced, and current great lakes remained. Most of the Lake Iroquois shoreline is south of here near Davenport, but a large bay existed in the Humber valley, and the shoreline of Lake Iroquois is revealed by walls of the Humber valley as far north as Hwy 401, and bounded by Black Creek and the Humber.
Regrowth of forest in the valley is capturing tons of carbon annually.