Toronto's Landform Region: The Ontario Lowlands

Toronto sits in the Ontario Lowlands (also called the Great Lakes–St. Lawrence Lowlands)—a fertile, flat-to-gently-rolling plain.

Geology

• Bedrock: Paleozoic sedimentary (limestone, shale, sandstone, dolostone) — 450–400 Ma.
• Surface: Glacial till, clay plains, drumlins, eskers, Lake Iroquois shoreline bluffs (Davenport Rd, Scarborough Bluffs).
• Origin: Eroded Canadian Shield + glacial deposition (Laurentide Ice Sheet retreat ~12 ka).

Hydrology

• Lake Ontario (south border) – moderates climate.
• Rivers: Humber, Don, Rouge, Credit – incised ravines (green corridors).
• Water table: High in clay plains; basements need sump pumps.

Human Impact

• Prime farmland → now >90% urbanized (Golden Horseshoe 9M+ people).
• Ravine system = 11,000 ha urban forest (world's largest).
• Subway/transit tunnels in shale (easy excavation).

Why It Matters

Lowlands = agriculture, settlement, transport. Toronto's existence as Canada's largest city is a direct consequence of this geology.