1872.] BAJISAY EIVER-COUKSES OF ENGLAND AND WALES. 155 



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 simulta- 

 neously and proportionately to the distance from the rise of the 

 river, because the further it flowed the more was its volume in- 

 creased by the aid of tributary streams and springs. Thus it hap- 

 I)ened 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 

 Eowsley 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 Avere 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 Eed 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 en- 

 croached 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. WTiether they did so or not does not materially 

 affect the next question to be considered; for if they did spread 



