﻿Yol. 6 1.] OF THE NORTHUMBERLAND AND DURHAM COALFIELD. 93 



of Eulwell and Cleadon Hills. They may possibly be remnants of 

 the Upper Chalk, which was (according to some authors) deposited 

 over a portion of the east of Durham, or they may have been, as 

 suggested by Richard Howse, brought over from Denmark by ice (2); 

 but it is more probable that they have been carried from an outcrop 

 of the Cretaceous rocks in the North Sea by the ice that once 

 occupied that area. 



The entire evidence deduced from the thickness and nature of 

 the Glacial deposits is in favour of the Glacial Period having been 

 long and protracted ; aud also the proofs given of the changes in 

 the courses of the rivers and of the post-Glacial valleys cut by 

 them, together with that of the amount of Boulder-Clay that must 

 have been removed to form the upper derived clay, river-terraces, 

 and raised beaches, are all in favour of there having been an interval 

 of considerable duration between the passing-away of the ice-sheet 

 and the present time. Indeed, the more I work upon the Glacial 

 deposits and post Glacial valleys of the two counties, the more am 

 I impressed with the length of time necessary for the production 

 of all the phenomena. 



It may not be out of place to note, that from the work done on. 

 the pre-Glacial valleys of Northumberland and Durham, it has 

 been found possible to show that there have probably been three 

 main cycles of river-development in the North-Eastern Counties of 

 England. The first between the end of the Permian and that of 

 the Cretaceous, when the point most worthy of notice is, that the 

 uplift of the Pen nines was probably accentuated in the Crossfell 

 area, so that the South Tyne, Wear, and Tees were developed from 

 a common centre; the second between the post-Cretaceous uplift 

 and the beginning of the Glacial Period, when the land stood higher 

 than at present, and the pre-Glacial valleys of the Tyne, Wear, 

 'Wash,' and others described in this paper, were formed, and the 

 contour of the pre-Glacial surface produced ; and the last after 

 the Glacial Period, during which the present courses of the rivers 

 have been developed, and the adjustment of the mountains, valleys, 

 rivers, and streams of the counties of Northumberland and Durham 

 evolved. 



YIII. Conclusions. 

 The principal conclusions drawn from this work are :-— 



(i) That Northumberland and Durham stood at a higher eleva- 

 tion in pre-Glacial times than at present. 



(ii) That a number of eastward-flowing streams had developed 

 a series of valleys, which are now filled up with superficial deposits 

 of very diverse character. 



(iii) That in pre-Glacial times the Tyne and Tees were the major 

 rivers, and all the other streams were tributary to them. 



(iv) That the higher parts of the pre-Glacial valleys of these 

 streams can be traced by field-work, and their lower reaches can be 



