THE GLACIAL GEOLOGY OF NORTHUMBERLAND 93 



chalk boulders (one striated) have been found in the boulder 

 clay at Walker and Heaton [20], and chalk flints in a com- 

 paratively stoneless clay (Howse's so-called Scandanavian 

 Drift) resting on the boulder clay proper at Tynemouth [1], 

 and in a similar clay at the foot of the Lyne Burn. 



Of far-travelled rocks, the most conspicuous are from the 

 Lake District and the South of Scotland. Representatives of 

 the former are andesites of the Volcanic Series of Borrowdale, 

 Threlkeld " granite," gabbro from Carrock Fell and the rock 

 of the Armboth Dyke. Many occurences of these rocks, 

 associated with Silurians, have been recorded in recent years 

 [20]. The northern limit of these rocks in the eastern part of 

 the county is, roughly, the divide between the Blyth and the 

 Wansbeck. West of this it passes through Sweethope and 

 along the Prestwick Burn. On the other side of the North 

 Tyne they have been traced by Dwerryhouse [16] as far north 

 as the Houxty Burn, though they are scarce north of the 

 Roman Wall. Isolated patches of drift containing andesites, 

 possibly of orrowdale origin, have been recorded as far 

 north as the Darden Burn [5]. 



Mixed with the Lake District rocks are many granites of 

 Scottish origin (Criffel, Dalbeattie) and red sandstones probably 

 of Permian age. They persist on passing northwards, after 

 the Lake rocks have died out, up to the fells of the western 

 border (Larriston, Caplestone, etc.). The drift of the Lewis 

 and Whickhope Burns contains, in addition to the Galloway 

 granites and Silurians, a great amount of a local, black, cherty 

 limestone. These rocks can be traced along the right bank 

 of the North Tyne to Bellingham, over the Wanny Crags 

 and down the Wansbeck as far as Morpeth. 



The drift of the Tweed Valley is particularly rich in Silurian 

 rocks ; to this source must be referred many of the boulders of 

 greywacke in the north-east of the county. 



No classification of the boulder clays of Northumberland 

 seems possible, though, locally, there is frequently evidence of 

 at least two clays of different origin. Thus a reddish clay 



