It is well known that in geologically recent times the British Isles have been affected by vertical movements, both upwards as shown by raised beaches and downwards as proved by submerged land surfaces and drowned valleys. There are still differences of opinion whether these movements result from changes in the level of the ocean surface or are due to real upward or downward movements of the land area. In the former case a change of sea level might be expected to produce within small limits the same amount of apparent elevation or depression of the land area, whereas in the latter case the amount of movement might vary at different parts of the coastline.