﻿88 DR. WOOLACOTT ON THE SUPERFICIAL DEPOSITS, ETC. [Feb. I905, 



evolved. The streams flowing entirely over the superficial deposits 

 must necessarily be of post-Glacial origin. 



Besides the pre- and post-Glacial valleys of Northumberland and 

 Durham, there are some minor valleys, sometimes totally or in part 

 dry, and generally cutting across the watershed between two main 

 watercourses, that are of special interest in connection with the 

 Glacial geology of the two counties. The valleys which they join 

 are, in all cases, of pre-Glacial development. I have seen several of 

 these, and examined two of them in detail, namely, the Beldon 

 Cleugh, running from the head of the Devil's Water into the 

 Derwent Valley, and Hown's Gill, cutting across the watershed 

 between the Derwent and the Brown ey ; and I am in agreement 

 with Capt, Dwerry house's interpretation of their origin (15), as 

 suggested by him in this Journal. It is shown in his paper that a 

 series of glacial lakes was formed during the Glacial Period in the 

 pre-existing tributary valleys of the Tyne, and that the straight- 

 cut channels, which have been developed across the watershed, are 

 the overflow-courses of these ice-bound waters. 



VII, Deductions. 



In the hollows occupied by the pre-Glacial valleys lie the above- 

 described superficial deposits, and, in between, the solid rock is (as 

 a rule) at or near the surface. In a few places, out of the trend 

 of the major valleys or on the higher ground, the rock is below or 

 but very little above sea-level, indicating in all probability that pre- 

 Glacial watercourses pass through these points ; a greater number 

 of borings, however, would be necessary before all these could be 

 accurately worked out. At many places between the main and 

 confluent valleys, the rock rises island -like out of its mantle of 

 Boulder-Clay and other deposits, and in the whole of the higher 

 portions of the western districts it comes to the surface. 



The valleys that had been formed before the Glacial Period were, 

 in all probability, but very slightly altered by the ice-movement 

 during that period. Their sides were smoothed and their contours 

 rounded ; but it seems certain that they were not appreciably 

 deepened, nor the general trend of their direction changed. Indeed, 

 except that they were wholly, or in part, rilled with the products of 

 the period, no changes of any very great moment were effected. 

 That some action did take place on the rock-surface we have evidence 

 in the ' Wash,' as (in the paper on that subject by Wood & Boyd) 

 the upper layers of a sandstone forming the bottom of this valley 

 are described as being ' furrowed and polished in rough and scored 

 outlines' (1). 



Prior to the period of glaciation, however, the dependence of the 

 contour of the country on its geological structure would be much 

 more pronounced than at present, as many of the minor features 

 have been more or less covered up by the products of that period, and 

 consequently in some cases obliterated ; and all the bolder features 

 have been softened. The borings and the field-work prove that the 



