Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/190

156 over part of these Carboniferous strata, they must have thinned away to a feather edge before the Oolitic escarpment began to be formed.

Taken as a whole, from the great escarpment of Carboniferous Limestone that overlooks the vale of Eden on the east, all the Carboniferous strata thence to the German Ocean have a gentle eastern dip—so gentle, indeed, that, on Mallerstang and other high hills overlooking the vale of Eden, outlying patches of the Lower Coal-measures or Gannister beds still remain to tell that once the whole of the Coal-measures spread across the country as far as the edge of the vale of Eden, and even far beyond, in pre-Permian times. These gentle eastern and south-eastern dips, caused by upheavalof the strata on the west and north-west, gave the initial tendency of all the rivers of the region to flow east and south-east; and thus it happens that the Tees, the Wear, the Derwent, the Tyne, the Blyth, the Coquet, and the Alne have found their way to the German Ocean, cutting and deepening their channels as they ran. The sides of these valleys, widened by time and subaerial degradation, now rise high above the rivers in the regions west of the Coal-measures, in a succession of terraces of limestone bands, tier above tier, as it were in great steps, till on the tops of the hills we reach the Millstone-grit itself.

We now turn to the western rivers of England, about which there is far less to be said.

First the Eden. This river flows through the whole length of the beautiful valley of that name, through Permian rocks, for nearly forty miles. At the mouth of the valley, at and near Carlisle, a patch of New Red Marl lies on the Permian Sandstones; and on the Marl rests the Lias. Whether the whole length of the Permian strata of the Yale of Eden was once covered by these rocks, it is impossible to determine; but I believe that it must have been so to some extent, and also that the Lias was probably covered by Oolitic strata. As these were denuded away by time, the Eden began to establish itself, and now runs through rocks in a faulted hollow in the manner shown in fig. 5 (p. 154). What is the precise date of the formation of this great valley and its river-course I am unable to say; but I believe that it may approximately be of the same age as the valleys last described. And so with the other rivers of the west of England, the Lune, the Ribble, the Mersey, and the Weaver—unless, indeed, some of these rivers, including the Dee, had their western courses determined by that western tilting of the strata that I believe originally established the greater part of the channel of the Severn.

I have already said that the rivers of Wales, the sources of the Severn, and all the other rivers that flow through the high Palaeozoic rocks are difficult to treat of in a definite manner; so highly disturbed are most of the rocks, and so ancient are those disturbances. The mountains there are, to say the least, pre-Permian, though it does not therefore follow that the present valleys date from that venerable age. The great tableland of South Wales, in