﻿Vol. 6 1.] SUPERFICIAL DEPOSITS, ETC. OE THE NORTHERN COALFIELD. 83 



down the valleys of the Deerness and the Browney from the west. 

 Both of these have a considerable thickness of Boiilder-Clay in 

 them ; the former 81 feet near Ushaw Moor, with the rock-surface 

 at an elevation of 219 feet ; and in the latter, quite near the river, 

 and opposite Witton Gilbert, is a boring showing 202 feet of super- 

 ficial deposits, with the rock-surface at an elevation of 93 feet. 

 From the east two other valleys, formed by obsequent streams, 

 joined the pre-Glacial Wear : one came down by Bowburn and 

 Shincliffe colliery — at the former of which localities there is 120 feet 

 of Boulder-Clay, while at the latter there is 174 feet, the rock lying 

 at an elevation of 126 ; and the other ran down from the Magnesian- 

 Limestone escarpment, passed between Pittington and West Sainton, 

 then through Sherburn, joining the Wear Valley a little to the south 

 of Durham. 



The pre-Glacial Wear thus appears to have received all the 

 waters from the west of Durham County, and taking up several 

 large tributaries between Bishop Auckland and Durham City, the 

 whole drainage was, immediately before the Glacial Period, poured 

 down the valley of the ' Wash,' and eventually into the pre-Glacial 

 Tyne. Not only does the evidence from the borings support this 

 hypothesis, as already explained in the description of the 4 Wash ' 

 (p. 79), but the field-evidence is entirely in favour of such a view. 



The Wear below Durham leaves the trend of its pre-Glacial course, 

 and passes over what was (before Glacial times) probably the water- 

 shed between the ' Wash ' and ' Cleadon ' Valleys ; thus it has 

 perforce developed an entirely-new valley since the Glacial Period. 

 The Wear, indeed, as in the case of many other of the rivers of post- 

 Glacial development, seems to have preferred to carve its way 

 through rock rather than over the superficial deposits ; the explana- 

 tion of this most interesting phenomenon will be discussed later 

 (p. 89). Its valley is cut deep through the Coal-Measures at Finchale 

 Abbey, and it flows over similar strata at Hylton, while at Sunder- 

 land it has carved a well-defined valley in the Permian rocks. 



The map of the pre-Glacial Wear, ' Wash,' and Tyne (PL IX) 

 enables the course and connections of these valleys to be traced, 

 and their depths can be ascertained from the numerous borings 

 shown. 



(d) The ' Sleekburn Valley/ (Figs. 7 & 8, pp. 82 & 84.) 



This valley is first distinctly proved by borings at Morpeth, at 

 which place the rock-surface lies at a depth of 13 feet below sea-level. 

 It may be traced through Choppington, Sleekburn, and Cambois, 

 reaching a maximum depth of — 93 feet at West Sleekburn Colliery. 

 At Cambois, which is nearer the sea, the solid rock is proved at 

 — 62 feet, but this may not be the maximum at this point ; or, it 

 may be that we have here evidence of Glacial or post-Glacial 

 movements, as in the case of the Tyne (p. 77). 



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