PhotoHunter: “Rock”

July 18, 2009 at 1:16 pm (Canada, History, Ontario, Ottawa, Ottawa River, Photographs, PhotoHunt, Prehistory)

My “rock” is part of the Canadian Shield. The Canadian Shield (aka the Precambrian Shield, or Laurentian Shield) is the Precambrian rock that covers about 8 million square kilometers of Eastern and Central Canada. It is comprised of some of the world’s oldest rock, dating back approximately 4.5 billion and 540 million years.

Some of that Precambrian rock.

Over successive ice ages, mountains (including some volcanic) as high and awesome as the Rockies have been scoured down to bare rock over which lies boreal forest. You can find evidence of the last ice age all over the place.

The view of the Laurentian mountains from Mont Tremblant, Quebec

In the photo below, you can see the edge of the Shield where it is cut off by the Ottawa River Valley, a great, wide valley which extends from the St. Lawrence River in the east and swings west and then northward towards Hudson Bay. It is a rift valley, formed when the bedrock dropped down tens of kilometres deep. Several major fault-lines run through the area and we experience frequent earth tremors, as a result.

View from the Champlain Lookout, in the Gatineau Hills

The edge of the Shield which bounds it on the northern edge rises up about 300 metres.

Parts of the Shield extend down into the US.

The Ottawa Valley and Canadian Shield

The Ottawa River Valley

The Ottawa Valley was once part of the great Champlain Sea, a huge brackish inland sea where whales once swam. The Champlain Sea formed when the great ice sheets of the last ice age pressed down on the land and when the melted, the Atlantic Ocean flooded in. When the last of the ice was gone, the continent tipped back and the water flowed out, again.