IOO DR. J. A. SMYTHE ON 



the complexity of movement of the various ice-sheets which 

 struggled for mastery during the glacial period in Northumber- 

 land. Much of the evidence is, at first sight, contradictory; 

 thus Cheviot rocks have been carried south, and sedimentary 

 rocks north on to the flanks of the Cheviots, and the striations 

 often give no clue to the origin of the neighbouring drift. 

 In the open country, where striations are almost exclusively 

 observed, it seems probable that they mark only the latest 

 phases of ice-movement, and only occasionally were con- 

 ditions favourable for the preservation of two series. The 

 interpretation of the data is thus a matter of considerable 

 difficulty and not a little uncertainty. Three stages of 

 glaciation can, however, be readily recognised, viz., the early 

 stage, the period of maximum glaciation and the period of 

 melting and retreat. 



At the beginning of glacial conditions, it is evident that the 

 Border hills between the North Tyne and Cheviot sent forth 

 considerable streams of ice in all directions. The ice from the 

 porphyrite area was hemmed in its western progression by 

 the ice from Carter and Peel Fells ("Carter Ice") and driven 

 down the left bank of the Redewater. The Carter ice was 

 similarly barred by the great western sheet of ice from the 

 Solway district and driven along the left bank of the North 

 Tyne. The three great streams converging near Redesmouth 

 were impelled in an easterly direction along the Wansbeck 

 and then south-east towards Tynemouth. The pressure of the 

 Solway ice evidently increased with time, the Carter ice 

 being driven towards the Coquet and the Cheviot ice diverted 

 until the Aln valley became the locus of its outflow. At 

 maximum glaciation it is probable that the western sheet held 

 complete sway almost as far as the coast. On the northern 

 side of the Cheviots, ice flowing down the Tweed valley seems 

 to have checked the flow of Cheviot ice in that direction and 

 to have surmounted even the outlying spurs of the hills. 



There is some evidence that a sheet of ice flowed southwards 

 along the coast at an early stage of glaciation. Towards the 

 end pressure from the North Sea had become a prime factor, 



