The Laurentian Divide separates the watershed of streams that flow north to the Arctic Ocean from the watershed of streams that flow south through the Great Lakes to the Atlantic Ocean. Here, the divide is formed by a prominent array of hills known as the Giants Range, a ridge that has been a highland for over two billion years. The name "Laurentian" is used because the granites forming the ridge are similar to, and were once thought to be related to, granites of the Laurentian Mountains in Quebec; although this connection is no longer considered true, the name has remained. The Giants Range is made up mostly of several types of granite formed several kilometers deep in the Earth's crust about 2.7 billion years ago. Uplift and erosion slowly brought the granites to the surface, and they have remained a highland because they are resistant to erosion. In the road cuts near the parking lot, crisscrossing bodies of darker and lighter granite record several successive intrusions of molten rock, and because of the complexity of the rocks, local geologists know this site as "Confusion Hill." About two billion years ago, the lower ground south of the highlands was covered by an ocean in which sediments were deposited, forming rocks that include the world-famous Biwabik Iron Formation of the Mesabi Range. About 80 million years ago during the Cretaceous period, sediments were again deposited in an ocean that lay south of the Giants Range. Between two million and 10,000 years ago, glaciers that advanced and receded across this terrain removed most of the Cretaceous sedimentary rocks, scoured the older underlying bedrock surface, and left behind deposits of silt, gravel, and boulders that now cover most of the bedrock.