pressure changes in the ice mass in the north. Continental ice sheets Ice caps Labrador Ice Sheet The Labrador Ice Sheet centered east of Hudson Bay. Expanding towards the southwest, it reached into the eastern edge of Manitoba and across the Great Lakes to the Ohio River, upwards of from its source. Its eastern lobes covered New England and reached south to Cape Cod and Long Island, New York. Ice lobes Keewatin Ice Sheet The Keewatin Ice Sheet began west of Hudson Bay in the Canadian Territory of Keewatin. The ice moved south some into Kansas and Missouri. To the west, it reached to the foothills of the Rocky Mountains. Cordilleran Ice Sheet The Cordilleran Ice Sheet has left remnants throughout the Northern Rocky Mountains. Unlike the other two ice sheets, this one is mountain based covering British Columbia and reaching into northern Washington State and Montana. The Cordilleran Ice Sheet has more of an Alpine style of many glaciers merged into a whole. The striations made by the ice field in moving over the bedrock show that it moved principally to the west through the passes of the coast range. Formation of proglacial and prehistoric lakes Whenever the ice sheet melted from the north at a moraine, water would begin to pond in the divide between a moraine and the ice front. The ice would act as a dam as water could not drain through the ice sheet, which in the Wisconsin period covered most of the proglacial river valleys. Numerous small, isolated water bodies formed between the moraine and the ice front. As the ice sheet would continue to melt and recede northward, these ponds combined into proglacial lakes. In areas without an available outlet, the water levels would either continue to rise until reaching one or more low spots along the rim of a moraine, or the ice sheet would retreat, opening access to a lower portion of the moraine. Multiple outlets could form through low spots too until one would become dominant after erosion lowered both the outlet and lake surface. Running water Ice melt and rainfall carried large quantities of clay, sand, and gravel from the ice mass. Clays could be moved long distances by moving water, while sand and gravel could not. Thus, sand and gravel landforms developed along the sides and front of the ice sheet; elongated accumulations of this material are known