Depressions come in all shapes and sizes. When weather forecasters talk about a depression off the coast of Norway, they refer of course to a meteorological phenomenon — one of those nasty low pressure cells that normally mean wind and rain. But Norway has another form of depression that is unique to the country: a great subterranean trench off Norway’s southern coast. If by some miracle the seas around Europe were suddenly drained, this feature would be the most striking piece of topography between Scotland and Scandinavia.