Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/189

1872.] seems so unnatural, that the late Mr. Hopkins, of Cambridge, stated that it was caused by two fractures in the strata running parallel to the winding course of the river. There are no fractures there of any importance. The true explanation is this. At an older period of the physical history of the country, the valley north and west of Buxton had no existence, and the land there actually stood higher than the tops of the limestone hills to the east. An inclined plain of denudation stretched eastward, giving an initial direction to the drainage of the country. The river began to cut a channel through the limestone rocks; and as it deepened and formed a gorge, the soft carboniferous shales where it rose also got worn away by atmospheric action, and from the north and west streams began to run into the Wye. By the power of running water those valleys all deepened simultaneously and proportionately to the distance from the rise of the river, because the further it flowed the more was its volume increased by the aid of tributary streams and springs. Thus it happened that the Wye seems unnaturally to break across a boss of hills which, however, were once a mere undulating unbroken mass of limestone. But there is no breakage, and nothing violent in the matter. It was a mere case of the wearing action of running water cutting a channel for itself from high to lower levels, till, where Rowsley now stands, it joined the Derwent, which flows in a long north and south valley scooped by itself chiefly in Yoredale shales, between the high terraced scarps of Millstone-grit and the grassy slopes of the Carboniferous Limestone.

When we come to the other rivers that enter the Humber north and west of the Trent the case is more puzzling. The Oolites in that region were extensively denuded before the deposition of the Chalk—so that between Market Weighton and Kirkby-under-dale, in Yorkshire, the Chalk is seen completely to overlap unconformably the Oolitic strata, and to rest directly on the Lower Lias, which is there very thin. The Chalk therefore overspread all these strata to the west, and lay directly on the New Red beds of the vale of York, till, overlapping these, it probably intruded on the Carboniferous strata of the Yorkshire hills further west, while the Oolites of the northern moorlands of Yorkshire also spread westward till they encroached on the Carboniferous slopes. The denuded remains of the latter now rise above the beautiful valleys of Yoredale and Swaledale, the whole, both Carboniferous and Secondary strata, having gentle eastern and south-eastern dips. These dips gave the rivers their initial tendency to flow south-east and east; and thus it was that the Wharfe, the Ouse, and the Swale, cutting their own channels, found their way to what is now the estuary of the Humber, while the escarpments of the Chalk and Oolite were gradually receding eastward to their present temporary positions.

That the Oolitic strata spread northward beyond their present edges is quite certain; but whether or not they extended far enough to cover the whole of the Durham and Northumberland coal-field, I am unable to say. Whether they did so or not does not materially affect the next question to be considered; for if they did spread