THE GLACIAL GEOLOGY OF NORTHUMBERLAND 107 



The Glacial Lakes North of the Coquet. — The dry valleys 

 north of the Coquet are divided into two great series, the 

 eastern and the western, and these are separated by the 

 Carboniferous uplands which form the great ridge of the 

 Chillingham Fells and the hills between the Aln and the 

 Coquet, stretching eastward as far as Alnwick Moor. Though 

 these uplands were completely overridden by foreign ice at 

 maximum glaciation, it is probable that the flow of native ice 

 from them was considerable during the melting stage. 



The Eastern Series. — After the clearing of the Lower 

 Coquet, the northern sheet retreated towards the Aln, its 

 western edge being confluent with the ice in that valley and 

 with that on the adjoining uplands. The swires marking 

 stages in this period are A 18 to A 22 (height of intakes 420, 

 360, 490, 250, and 400 feet). Some of these, A 19, A 20, and 

 A 21, are of great depth, pointing to slow recession of the ice. 

 North of the Aln, two channels of moderate size, A 23 (350 

 feet) and A 24 (380 feet) give evidence of the position of the 

 northern sheet. A small kaim, thrown half way across the 

 latter slack, marks a temporary advance of the ice in this 

 region. Beyond Belford the country has not been examined 

 in detail. 



The Western Series. — This great series of swires requires for 

 its interpretation the co-existence of three ice-sheets, evidence 

 of which has been already given. These are the northern 

 sheet, sweeping down the Tweed valley along the northern 

 flanks of the Cheviots and diverted up the valley of the Till ; 

 the Cheviot ice flowing in particular down the Breamish valley 

 and forced eventually into the valley of the Aln; and the 

 western sheet, impelled from the Redewater, overriding the 

 southern flanks of the Cheviots, towards the head of the Aln. 

 These sheets cleaved in the neighbourhood of Ingram, and in 

 their retreat produced striking effects. The northern sheet 

 blocked up the Breamish valley, forming a lake which drained 

 across the watershed into the Aln, the huge gorge of Shawdon 

 Dene, C 1 (300 feet), being thus eroded. The retreat of this 

 sheet northwards and westwards corresponded with the 



