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:''This article is about an ecozone. For the landform covering the same region, see Canadian Shield. The Boreal Shield Ecozone is the largest ecozone in Canada. Covering 1.8 million square kilometres it covers almost 20% of Canada’s landmass, stretching from northern Saskatchewan to Newfoundland. ==Formation== Canadian Shield rock forms the nucleus of the North American continent. Other geological structures assumed positions around or on top of the Shield millions of years after it was formed. The Rocky Mountains are relative newcomers on the geological stage. Most Shield rocks were formed well over a billion years earlier, during the very first chapter of the planet's history known as the Precambrian era. What once may have been a towering mountain chain is today a great rolling plain of ancient bedrock. During the late Precambrian era, fierce convulsions in the Earth’s crust resulted in a warped, collapsed Shield. The foundation of much of the ecozone is now metamorphic gneiss, a highly banded rock formed by intense pressure and heat. Many of the minerals that contribute to the Shield’s economy may have formed during these geologically turbulent times. During the last ice age, which ended 10 000 years ago, the advance of glaciers continuously plucked and scoured the Boreal Shield, forming striations in the bedrock and carrying large boulders many kilometers. In retreat, massive glaciers enveloped most of the landscape with great amounts of glacial deposits including gravel, sand, shale, and numerous sediments. The vast majority of inadequately drained depressions that were left behind, as well as natural faults in the bedrock, now form the millions of lakes, ponds and wetlands that give this ecozone its distinctive character. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Boreal Shield Ecozone (CEC)」の詳細全文を読む スポンサード リンク
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