192 ON CEKTAIN SUEFACE FEATURES OF THE 



thickness, reachiug high up the slopes of the valley ; that it is 

 commonly carved into river-terraces, often sharp in outline even 

 at the highest level above the present Thahoeg ; that much false- 

 bedding is exhibited — coarse-boulder beds, moderate-grained 

 gravels, and fine sands, rapidly alternating with no regularity of 

 order — and that a large number of the rounded boulders which 

 it contains appear to be of Scottish origin, a smaller number 

 belong to rock-types of the Lake district, and the rest may be 

 referred to local sources. Many of these boulders are polished 

 and scratched. 



The bluffs on both sides of the Tyne show excellent sections, 

 but the points to which I am anxious to direct attention can be 

 best studied on the northern or left bank of the river between 

 Thornbrough Wood and the Styford alluvial flats or haughs. 



The river is here rapidly eating back the land, and the cliff- 

 like face is year by year receding further to the north. This 

 ordinary denuding action is greatly facilitated by numerous 

 irregular springs which are thrown off here and there by the 

 more or less clayey layers common in the sands and gravels, as 

 they crop out in the nearly vertical scarp. A more constant 

 and better defined line of springs occurs at the junction of the 

 sands and gravels with the underlying Boulder Clay. 



I have been led of late to pay special attention to the variable, 

 but by no means small, outflow of water which, by means of 

 these many springs, takes place from the land to the river. Con- 

 sidering the incoherent character of much of the deposits and 

 the steepness of the bluffs it is not easy to note with accuracy 

 how much sediment from tvtthin the hill is carried away by the 

 springs, or to distinguish such sediment from the exactly similar 

 material which is merely washed down after the issue of the 

 water. By repeated observation, however, both during drought 

 and after heavy rains, and at different seasons of the year, I 

 have satified myself that a very notable amount of sand and very 

 fine gravel is continually being discharged at very varying rates 

 from underground. In other words it is clear that the sands 

 and gravels are being actively removed from within as well as 

 denuded from without. 



