﻿Vol. 6 I.] OF THE NORTHUMBERLAND AND DURHAM COALFIELD. 65 



their exact position accurately mapped ; the depth of the surface- 

 deposits has also been worked out, and their character has been 

 studied. 



The actual number of borings of which reliable data were avail- 

 able, and could therefore be used for the purpose of this inquiry, 

 was about 600, but several hundred others gave confirmatory 

 evidence. The remainder, although carefully gone over, did not 

 prove to be of much service, because the facts obtained from them 

 were always uncertain. It has, however, been found possible to 

 obtain exact information regarding the thickness and character of 

 the Glacial deposits ; to gain a rough idea of the contour of the 

 country before Glacial times; to form a more accurate conception of 

 the drainage of that period ; and also to work out more thoroughly 

 the relative changes of level before, during, and after the Glacial 

 Period. 



II. The Nature of the Deposits. 



The superficial deposits of the great Northern Coalfield may be 

 roughly divided into three main parts, namely: — 



(a) The stony Boulder-Clay. 



(b) The Upper Clay, which has been generally derived from the lower 



stony clay, and is broadly divisible into two portions: — (1) The 

 prismatic clay, and (2) the leafy clay. 



(c) Deposits of sand and gravel occurring below, in, or upon the Boulder- 



Clay. 



(a) The Stony Boulder-Clay. 



The first, which is the only kind that should be called ' Boulder- 

 Clay,' is a firm unstratified clay, full of stones, varying in weight 

 from a few grains to several tons. It may be examined in several 

 sections along the coast, but perhaps best at Whitley, north of 

 Cullercoats ; between North Shields and Tynemouth, on the banks 

 of the Tyne ; and at Hendon, a mile south of Sunderland. It is 

 sometimes seen resting directly upon the surface of the solid rock, 

 although often there is a breccia, consisting of local fragments, 

 intervening between it and the rock-surface. Sand and gravel are 

 also proved to occur beneath it in some of the borings. This clay 

 is often present as one complete mass, reaching in some cases a 

 thickness of over 100 feet with little or no change in character, 

 except that the lower parts of it generally contain more boulders 

 than the upper ; very frequently, however, deposits of sand and leafy 

 clay are intercalated in it. Throughout nearly the whole district its 

 colour is brownish or bluish, but south of Castle-Eden Dene the 

 clay becomes distinctly red and sandy. Some of the boulders 

 occurring in it are local, more especially near the base ; but a very 

 large number foreign to the district are also found therein, 

 being principally derived from the district lying to the north and 

 west. Pieces of Bernician Limestone, Whin Sill, and Cheviot 

 Porphyry are especially common ; but while something has been 

 done towards a classification of the boulders in the different super- 



Q. J. G. S. No. 241. f 



