Continental shield, any of the large stable areas of low relief in the Earth’s crust that are composed of Precambrian crystalline rocks. The age of these rocks is in all cases greater than 540 million years, and radiometric age dating has revealed some that are as old as 2 to 3 billion years.Shield areas in general are regarded as continental nuclei, the observation often being made that most continental shields are bordered by belts of folded rocks of post-Precambrian age.Continental shields, as the name implies, occur on each of the continents. One of the best known is the Canadian Shield, which extends from Lake Superior on the south to the Arctic Islands on the north, and from western Canada eastward, to include most of Greenland. In South America, the principal shield area is called the Amazonian Shield. It occupies much of the eastern bulge of the continent. Smaller areas of Precambrian rocks to the north and south of the Amazonian Shield are designated the Guiana and Platian shields, respectively. Shield provide stable landmass and is a source of minerals, ores etc. They also act as a source of raw material for construction apart from it they also provide fertile soil for agriculture.