Thursday, October 17, 2019
GEOLOGICAL HISTORY OF CANAD Essay Example | Topics and Well Written Essays - 1000 words
GEOLOGICAL HISTORY OF CANAD - Essay Example The first class consists of sedimentaryà rocks which form the Earths surface. Some consist of fragments that vary in range and are eroded from olderà rocks and deposited as gravel, sand or mud and are then consolidated by burial yieldingà 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. Sedimentaryà rocksà makeà upà 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 rocksà have petrified remains of animals and plants (fossils), and olderà rocksà contain diverse kinds of fossils compared to youngerà rocks. Igneousà rocksà 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. Metamorphicà rocksà formed when igneousà or sedimentary rocksà 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 Earthââ¬â¢s core. Consequently, limestone changed to marble, shale to schist, and platonic rock to gneiss. Metamorphicà rocksà are common in the Shuswap Highland, the Coast Mountains and the Columbia, Omineca and Cariboo ranges of the eastern Cordillera. The presence of metamorphicà rocksà at the surface is the evidence of those parts of the
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