GEOLOGICAL HISTORY OF CANAD - Essay Example

The first class consists of sedimentary rocks which form the Earths surface. Some consist of fragments that vary in range and are eroded from older rocks and deposited as gravel, sand or mud and are then consolidated by burial yielding conglomerate, sandstone or shale respectively. Others comprise of chemical deposits, for example gypsum or rock salt, which resulted from evaporation of seawater. Still others result from biological activities, for instance cemented shell fragments or coral reefs form limestone.

Sedimentary rocks make up the easternmost ranges of the Canadian Cordillera known as the Mackenzie, Rocky and Franklin mountains, but are common in the western Cordillera as well. Many sedimentary rocks have petrified remains of animals and plants (fossils), and older rocks contain diverse kinds of fossils compared to younger rocks. Igneous rocks originated deep within the Earth as molten rock or magma. Magma that solidified deep within the earth formed platonic rock such as granite, which is a common rock particularly in the coast mountains of the western Cordillera and are widely distributed elsewhere.

Magma that emerged as lava and cooled at the Earths surface formed a variety of volcanic rock, which is widespread in the interior plateau region and elsewhere in the western Canadian Cordillera. Metamorphic rocks formed when igneous or sedimentary rocks were buried deep within the Earth during mountain formation. New minerals grew while old features of the rock were destroyed in response to the high temperatures and pressures encountered in the Earth’s core. Consequently, limestone changed to marble, shale to schist, and platonic rock to gneiss.

Metamorphic rocks are common in the Shuswap Highland, the Coast Mountains and the Columbia, Omineca and Cariboo ranges of the eastern Cordillera. The presence of metamorphic rocks at the surface is the evidence of those parts of the