<P> The North American craton is the bedrock forming the heart of the North American continent and the Canadian Shield is the largest exposed part of the craton's bedrock . </P> <P> The Canadian Shield is part of an ancient continent called Arctica, which was formed about 2.5 billion years ago during the Neoarchean era . It was split into Greenland, Laurentia, Scotland and Siberia and is now roughly situated in the Arctic around the current North Pole . </P> <P> The current surface expression of the Shield is one of very thin soil lying on top of the bedrock, with many bare outcrops . This arrangement was caused by severe glaciation during the ice age, which covered the Shield and scraped the rock clean . </P> <P> The lowlands of the Canadian Shield have a very dense soil that is not suitable for forestation; it also contains many marshes and bogs (muskegs). The rest of the region has coarse soil that does not retain moisture well and is frozen with permafrost throughout the year . Forests are not as dense in the north . </P>

What are the geographical features of the canadian shield