OF PHYSICAL GEOGRAPHY. 9 



away the loosened grains of every kind, rills collect, and rivers 

 carry away the accumulated detritus, and the rough old sea 

 channels, in some places filled up by these deposits, and in 

 others worn still deeper, are changed into those smooth dales or 

 picturesque glens, which are the boast and charm of the North. 

 Rivers run in valleys which the sea made for them. 



The rivers, therefore, in their higher parts, for the most 

 part run with the inclination of the strata. Hence easterly and 

 south-easterly courses of the streams are the most common in 

 Yorkshire, but when the dip of the strata is eastwardly in one 

 part and southerly in another, the rivers run in one part to the 

 east, and in the other to the south. The Derwent which rises 

 by many branches on the north side of the Vale of Pickering, is 

 a striking example. The main ridges of hills do not necessarily 

 run between the rivers : they more frequently range parallel to 

 the axes of elevation, which are for the most part summits of 

 drainage ; but ranges of high ground also, not seldom, cross 

 the courses of many rivers, in terraces which are escarped toward 

 the source of the stream, in the north or the west, but have 

 longer, easier, and less picturesque slopes to the east or the 

 south. The explanation of this circumstance is found in the 

 nature of the alternating strata. In such hills, the edge of the 

 escarpment is usually the termination of a broad area of hard 

 or well consolidated rock, while softer clay or shale appears 

 below. Such materials being brought by this upward movement 

 of the sea bed within the action of the water, would be wasted 

 unequally the soft beds more, the hard beds less ; so that deep 

 hollows would be produced in a direction across the line of the 

 main channel or sea valley. These hollows often suggest at the 

 present day the notion of former lakes with barriers situated at 

 the gorge formed by continuous rocks, which barriers the river 

 now flowing is supposed to have cut through and thereby to 

 have drained the lake. Such effects may have happened, but 

 the general explanation is that given above. 



Thus were formed the remarkable escarpments or ' nabs ' 



