A low-lying area which is wholly or largely surrounded by higher land. An example is the Hudson Bay in northeastern Canada, which was formed by depression beneath the centre of a continental ice sheet 18,000 years ago. Another example, the Qattara depression, is 150 mi (240 km) long and the largest of several wind-excavated basins of northern Egypt. Depressions in the ocean floor are also basins, as the Canary Basin, west of northern Africa, or the Argentine Basin, east of Argentina. These basins occur in regions where cold, dense oceanic crust lies between the topographically elevated ocean ridges and the continental margins.