﻿90 I)E. WOOLACOTT ON THE SUPERFICIAL DEPOSITS, ETC. [Feb. I905, 



at broadly, have been convexly curved, but also some time after its 

 formation it probably lay in ridge-like mounds, as it does at present 

 in the Vales of York and Eden, although there are few traces of 

 such in the district under discussion. Near Gosforth, and one or 

 two higher parts of the country, the surface lies in long ridges, but 

 (as a rule) the whole area is perfectly flat. This levelling-out of 

 the Drift is most noticeable near the coast-line, and was probably 

 produced by marine action at the time of the depression marked by 

 the raised beaches of the district. 



That a great thickness of the Drift has been removed is evident; 

 and Prof. Lebour has suggested that it is probable that the true 

 method of obtaining a correct measurement of the total thickness 

 of it in the valleys immediately after its production, is by finding 

 the highest contour at which it exists along the sides of the valley 

 and the maximum depth at which it occurs at its base. This 

 would give us an approximation to its true thickness, although, 

 owing to the amount that may have been removed from the flanks 

 of the valleys, and its probable convexly-curved surface, its total 

 dimensions may have been much greater. In the ' Wash ' the 

 Boulder-Clay creeps up to an altitude of between 400 and 600 feet, 

 and is found at a depth below sea-level of about 140 feet ; it would 

 thus seem that, in all probability, there must have been some 600 

 to 700 feet of superficial deposits in this valley. The step-like 

 river-terraces of the upper Tyne, which have been formed since 

 the Glacial Period, and occur up to and beyond the 300-foot contour- 

 line (thus high above the present level of the river), support this 

 conception of the thickness of the superficial deposits, as it is 

 manifest that they must have been produced from the Drift that 

 once filled the pre-Glacial valley (6). 



All the present courses of the rivers are of post-Glacial develop- 

 ment ; some, however, flow along the line of the pre-existing valleys. 

 The Tyne, although deviating here and there from the course of the 

 old valley, follows in the main the general trend of it ; while the 

 Team flows along the course of the ' Wash.' The general direction 

 of the Derwent and the upper parts of the Wear and its tributaries 

 is unchanged ; but the lower part of the latter river, from Durham 

 downward, has been entirely cut through Boulder-Clay and Carbo- 

 niferous and Permian strata, since the end of the Glacial Period. 

 The Blyth and the Wansbeck are also post-Glacial in origin, and 

 have been developed mainly through rock. The present valley of 

 the latter river affords striking evidence of the amount of denudation 

 that has taken place since the Glacial Period : its narrow, deep, 

 straight-cut valley having been entirely denuded in Carboniferous 

 rocks since that time. It has also been indicated that the lower 

 reaches of the Coquet are of similar development, and thus analogous 

 evidence can be deduced from this river. 



Along the coast from Warkworth to Sunderland several wide, 

 sweeping, sandy bays occur ; these are the points where the 

 Boulder-Clay reaches the sea, and they mark the outlet of the pre- 

 Glacial valleys or lower parts of the rock-surface. The principal 



