﻿Vol. 6 1.] OF THE NORTHUMBERLAND AND DURHAM COALFIELD. 75 



Locality. 



Valley. 



Depth of 



rock-surface 



below sea-level. 



1. Burdon Main 



Tyne 



Feet. 

 -141 

 -140 

 -125 (?) 

 -116 

 -108 



- 93 



- 93 



- 75 . 



- 62 



2. Norwood New Pit 



'Wash' 



3. Blaydon ... 



4. Lames! ey 



Tyne 



'Wash' 



5. Kibblesworth 



'Wash' 



6. Sleekburn 



' Sleekburn ' 



7. Percy Main 





8. Chirton 



9. Cainbois 



Tyne 



' Slfifikhiirn ' 



i 



The maximum depth below sea-level at which the rock-surface is 

 met is about 140 feet ; and, judging from the number of borings, it 

 is probable that this is about a true maximum. The height of the 

 land is thus proved to have been in pre-Glacial times much greater 

 than at present, and therefore the valleys in which 'the superficial 

 deposits lie are the valley-track of a river-system, the streams 

 having had their source in the Cheviots and Pennines, and the 

 constructional shore-line lying far to the east of its present position. 

 Indeed, at one time they may have been all tributary to a major 

 stream running down the centre of the area now occupied by the 

 North Sea (7). What the difference in height was we have no 

 means of exactly judging, but that it was considerably over 140 feet 

 higher is tolerably certain. Prof. James Geikie shows that, before 

 the Ice-Age, Scotland stood at an elevation of from 300 to 600 feet 

 greater than at present (3), and the borings discussed in this paper 

 seem to point to a somewhat similar elevation for our part of the 

 country. 



The principal pre-Glacial valleys were seldom entirely obliterated, 

 because their lower portions only were filled with Boulder-Clay ; but 

 the disappearance of some of the minor ones was complete. The 

 ' Sleekburn Valley' (see p. 83) was entirely filled up, .and could not 

 be determined from the surface of the country ; but the pre-Glacial 

 Tyne, the < Wash,' and the upper part of the Wear were only 

 partly masked by the covering of Glacial deposits, and thus the solid 

 rock still flanks the higher parts of these. 



V. The pre-Glacial Valleys. 

 The principal pre-Glacial valleys and depressions are : — 



(«) The Tyne and its tributary valleys. 

 (6) The 'Wash.' 



(c) The Upper Wear and its tributary valleys. 



(d) The ' Sleekburn Valley.' 



(e) The depression running out at Druridge Bay— the ' Druridge 



Valley.' 



As these valleys are all fairly distinct one from the other, it will 

 perhaps be best to give a detailed description of each, and to discuss 

 their mutual connections as occasion arises. 



