Surficial Geology

Surficial Geology

Surficial geology, also referred to as Quaternary geology, refers to those unconsolidated geologic materials lying on top of the bedrock.

Although the Quaternary era covers the last 1.81 million years of earth history, in Ontario almost all surficial sediments are much younger (<45,000 years old). The sediments were deposited either during or after the last glacial period. Common surficial materials include:

  • Sand and gravel
  • Glacial tills
  • Clay and silts

Ontario Geological Survey

The Ontario Geological Survey is responsible for producing maps and reports that describe the type and distribution of the surficial deposits in order to:

  • Assist with resource evaluations such as groundwater assessments and aggregate inventories.
  • Provide a framework for mineral exploration involving the use of overburden (drift) samples.
  • Identify terrain (land) features and characteristics that are of ecological importance or affect public health and safety.


Knowledge of Ontario’s surficial geology is important as it influences many aspects of life, industrial growth and recreation. The types of material forming the ground surface affects, for example, agricultural practices, how and where we build roads and communities, and the flow and quality of surface and groundwater.

Development on the surface of the Earth requires an understanding of surficial geology. Mapping of the surficial sediments identifies resources, such as sand and gravel used to produce construction aggregates, and underground water sources (aquifers) that supply human needs.

Environmental management and land stewardship also benefit from information provided by surficial mapping. Mapping outlines ecologically sensitive terrains, hazard lands and areas vulnerable to disturbance.