Large parts of North America was periodically covered by Cordilleran Ice Sheet.
== Sea levels during glaciation ==Because of the weight of the ice, the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today (measured by the level of bedrock)
  The difference between it and true north is called the magnetic declination (or simply the declination where the context is clear)

