Bedrock Geology

Bedrock Geology

Bedrock geology is a general term that refers to the solid rock that lies beneath the soil and other surficial materials like sand and gravel. Bedrock geology is a major influence on the surface features and drainage patterns of the Earth. The bedrock geology of Ontario can be divided into two broad types based on age.

The Precambrian Canadian Shield consists of very old, resistant rocks that range in age from 570 million to more than 3 billion years old. The rocks of the Canadian Shield consist of crystalline igneous, sedimentary and metamorphic rocks that have had a complex history of volcanic eruptions, mountain building, faulting, deformation, burial, uplift, weathering and erosion. These rocks contain the majority of Ontario’s metallic mineral deposits in areas known as “greenstone belts” because they are dominantly composed of green or gray volcanic and sedimentary rocks.

Ontario’s bedrock is also composed of younger Paleozoic and Mesozoic sedimentary rocks that range in age from 63 to 570 million years old and contain valuable deposits of salt, gypsum, oil, natural gas, groundwater, shale, lime, building stone and aggregate. These rocks were deposited in large sedimentary basins during long periods of sedimentation that also saw the development of life forms from simple algae through primitive marine invertebrates to dinosaurs and mammals. Paleozoic and Mesozoic rocks underlie the Hudson and James Bay lowlands of northern Ontario, and the St. Lawrence and Great Lakes lowlands of southern Ontario including the Niagara Escarpment.

Ontario Geological Survey

The Ontario Geological Survey is responsible for describing the types, characteristics, distribution, and history of the bedrock in order to:

  • Provide a framework for mineral development by documenting areas with favourable mineral potential.
  • Provide geoscience data for effective and informed land-use planning.
  • Provide a better understanding of the history and evolution of Ontario’s geology and the Earth’s crust.


Ontario Geological Survey bedrock geology maps can be used to influence land use and development by identifying:

  • Areas of high mineral potential which attract mineral, oil and gas investment
  • Faults in the bedrock that control the flow of groundwater
  • Rock types that can be used for building stone and road construction
  • Areas of high mineral concentrations which may pose a health risk.

Bedrock geology maps are also used as a foundation for further detailed geoscience research by universities and colleges and as educational tools for the general public at museums and science centres.