Tilting actually. As the Canadian shield rises, the lands to the south drop to equalize.
Its like when you sit on a couch next to a fat chick. She causes a depression in the surface with your body forced to lean down toward it but when she gets up you equalize. Fat Chick Physics.
Fat Chick Physics: sweet potato pie with marshmallows, breaded fried pork fat, and “sum ‘nana puddin’.”