this region is of such moderate elevation above the sea, that it would be almost equally laid under water, were there a sinking of no more than 600 feet.
To make this last proposition clear, I have constructed, from numerous documents, many of them unpublished, the map, fig. 40, given at p. 278, which shows how that small amount of subsidence would reduce the whole of the British Isles to an archipelago of very small islands, with the exception of parts of Scotland, and the north of England and Wales, where four islands of considerable dimensions would still remain.
As to the district south of the Thames and the Bristol Channel, it seems to have remained land during the whole of the glacial period at a time when the northern area was under water.
The map, fig. 40, p. 278, just alluded to, represents simply the effects of a downward movement of a hundred fathoms, or 600 English feet, supposed to have been uniform over the whole of the British Isles. It shows the very different state of the physical geography of the area in question, when contrasted with the results of an opposite movement, or one of upheaval, to an equal amount, of which Sir Henry de la Beche had already given us a picture (from which I have borrowed the map, fig. 41, p. 279), in his excellent treatise called 'Theoretical Researches.'[1]
If we are surprised when looking at the first map, fig. 40 at the vast expanse of sea which so moderate a subsidence as 600 feet would cause, we shall probably be still more astonished to perceive, in fig. 41, that a rise of the same number of feet would unite all the British Isles, including the Hebrides, Orkneys, and Shetlands, with one another and the continent, and lay dry the sea now separating Great Britain from Sweden and Denmark.
- ↑ Also repeated in De la Beche's Geological Observer.
