106 DR. J. A. SMYTHE ON 



swires outside of the Cheviot area (Photograph 3 and map 

 No. 2). The next stage of withdrawal corresponded to the 

 clearing of the ice between the Whiskershiels and Fallowlees 

 Burn, the consequent cutting of B 8 (1,010 feet), B 9 (950 feet), 

 the marginal channels near Eastnook on the right bank of the 

 Whiskershiels valley, and eventually the huge swire B 10 (630 

 feet) at the head of the Grasslees Burn. Meanwhile the edge 

 of the great sheet was retreating along the high land between 

 the Fallowlees and Hart Burns, and was next in a position 

 to impound water when it lay across the broad, drift-filled 

 valley of the Delf Burn. The overflow was now over the 

 Rothley Crags, and the deep gill of that name, B 11 (650 feet), 

 was cut. Similar conditions would again hold two miles 

 south of this position, and would result in the formation of the 

 post-glacial valley of the Hart Burn. 



Indications of the last stages of retreat of the western ice 

 east of the North Tyne are found on the Ottercaps and in the 

 Erring Burn valley. The Ottercaps ice evidently became 

 independent and sent small tongues of ice down the adjacent 

 valleys. The moraines in the Lisles Burn and Whiskershiels 

 valley are evidence of a westerly flow from this ice-cap. In 

 the Erring Burn valley two positions are marked by the swires 

 B 12 (680 feet) and B 13 (650 feet). Possibly some of the 

 notches in the Whin Sill, as at New Onstead near Bavington 

 (B 14), were produced then. At this stage the direction of 

 movement had changed slightly, possibly owing to expansion 

 of the Tyne glacier following upon the relaxation of pressure 

 from the main western sheet. The ice was thus pushed in a 

 direction somewhat north of east, parallel to the outcrop of the 

 Whin Sill. A recorded striation in the district near Bavington 

 and the divergence in composition of the upper gravels from 

 the boulder clay, as commented on above, confirm this view. 

 West of the North Tyne there is little record of the retreat of 

 the Solway ice, and the contour of the country and direction 

 of retreat would lead one to expect little. On the western 

 watershed, however, opportunity again occurred for the forma- 

 tion of an ice-dammed lake, and the record of this is the great 

 swire near Gilsland (Mackinder's "Tyne Gap.") 



