NATURAL ENVIRONMENT

A massive dome of Precambrian rock dominates the Canadian landscape. Called the Canadian Shield, it lies at or near the surface of the Earth. Shaped somewhat like a giant inverted saucer, it sweeps from the Amundsen Gulf southward and eastward across the top of the Prairie Provinces, around Hudson Bay to the Atlantic Ocean, encompassing most of Ontario and Quebec and all of Labrador. The sedimentary rocks that make up the remainder of the country's surface and near surface rest on this ancient base, though it may be necessary to penetrate deeply into the Earth to find it.

In the Paleozoic era (570 million to 225 million years ago) and later in the Mesozoic era (225 million to 65 million years ago), ancient seas invaded the depressed areas of the Canadian Shield and gradually formed layer upon layer of sediment. In the course of millions of years, these layers were solidified, then uplifted and broken by tremendous geologic forces. Tiny marine life trapped in the sediment formed oil and natural gas deposits that gathered in the folds of the rock. Giant dinosaurs also were covered, and they too became part of the rock layers.

Some rock was melted and re-formed, and some molten rock invaded the massive cracks in the Earth's crust, where slowly it cooled and formed massive deposits of minerals. Wind and water and glacial ice wore away the rock, laying down the particles in valleys and depressions, where over the centuries living organisms have turned it into soil.