The Great Lakes of North America, four of which form the border-line between the United States and the Dominion of Canada, increase in size from east to west, Lake Ontario being the smallest but still 180 statute miles in length. Lake Erie is the shallowest, with an east to west extent of 236 statute miles. Lake Huron has a maximum length of 247 statute miles from south to north. Lake Michigan is the only one of the lakes entirely within the confines of the United States, extending 321 statute miles from north to south. The largest and deepest of the group is Lake Superior, where the principal sailing course from Sault Ste. Marie to Duluth is 383 statute miles.