﻿Vol. 6 1.] OF THE NORTHUMBERLAND AND DURHAM COALFIELD. 67 



the production of the raised beaches which are described hereafter 

 (p. 69). This clay can be especially well examined in the numerous 

 brickfields around Sunderland, and along the line of the Cleadon pre- 

 Glacial valley, h aviug been here produced by the last-named cause. The 

 relationship between the prismatic clay which occurs at the surface of 

 Boldon Flats and the neighbouring district, and the raised beaches 

 exposed on Cleadon Hill and Fulwell Hill, seems to me to be indis- 

 putable. This is shown in the section drawn between these two hills 

 (fig. 1, p. 66), which illustrates a pre-Glacial valley, carved in Permian 

 rocks, and filled with stony Boulder-Clay overlain by prismatic clay. 

 Clay of this nature is also found in the north of Northumberland, 

 there being a fine exposure of it in Birling Quarry, near Warkworth, 

 a photograph and description of which were given by Prof. E. J. 

 Garwood in ; The History of Northumberland ' vol. v (1899) p. 12. 



(2) The leafy clay that occurs in many parts of the district, 

 as in the ' Wash ' and round Newcastle, lying above the Boulder-Clay, 

 associated with deposits of sand and sandy clay, is also probably 

 a water -formed deposit, and may have been laid down in 

 lakes at the end of the Glacial Period. Prof. Lebour discusses, in 

 a ' Note on a small Boulder, found in the later Glacial Deposits in a 

 Wash-out near Low Spen, in the Derwent Valley ' (16), the origin 

 of this formation, and shows that it was deposited in a lake ; and 

 Mr. G. Brennan has obtained tracks of freshwater Crustacea from it. 



(c) Deposits of Sand and Gravel occurring below,, in, or 

 upon the Boulder-Clay. 



This type of deposit is fairly widespread, and may occur in three 

 distinct positions, each having had a separate origin. Those found 

 below the Boulder-Clay, as in the valley of the 'Wash,' were possibly 

 formed by pre-Glacial rivers and streams, or by the torrents that 

 must have flowed at the commencement of the Ice-Age from the 

 higher valleys, when they were ice-filled and the lower valleys were 

 not so filled. The most remarkable, however, of the deposits lying 

 in this position is exposed on the Northumberland coast, north of 

 the mouth of the Wansbeck. It consists mainly of coarse gravel 

 containing flints, and rests upon the solid rock-surface. Since it is 

 overlain by Boulder-Clay, it was formed before or during the Glacial 

 Period, and may be either a raised beach or an old river-terrace 

 (fig. 2, p. 68); but, as the height o£ the land was greater before 

 and during that period than it is now, I am inclined to the latter 

 view. The occurrence in it of flints and other rocks foreign to the 

 drainage-area of the pre-Glacial stream does not, however, lend 

 support to this contention ; indeed, the nature of this deposit is 

 not yet quite understood. 



The deposits of sand and sandy and leafy clay that are found 

 embedded in the true Boulder-Clay were most probably formed by 

 streams of water, which, resulting from the melting of the ice, would 



f2 



