BETWEEN THE TYNE AND THE WANSBECK 95 



which is to isolate rounded hummocks of rock, encircled , by , 

 what on lower ground would be oxbows.* 



According to Kendall's hypothesis these slacks or swires 

 (see footnote) may be regarded as the forsaken channels of 

 streams which had a temporary existence during the last 

 stages of the Glacial Period, such streams being the overflow- 

 waters of lakes formed by the impounding of drainage in 

 valleys by ice-sheets which still lingered on the lower ground. 



To apply this hypothesis to the case in question we must 

 assume that at one stage in the passing of the great ice-sheet 

 with which the country was clad in glacial times, the high 

 land above, say, the 400-foot contour was relatively free from 

 ice, v/hile the lower land east of this was still buried under an 

 ice-sheet, which moved in a general southerly direction, the 

 western edge of this sheet stretching in a line roughly from 

 Heddon Laws to Bolam. This would serve as a barrier to 

 the escape of the waters of all the eastwardly flowing burns in 

 the Pont-Blyth area, and would produce a lake bounded on 

 the north by the Whalton Ridge, on the east by the ice-sheet, 

 on the south by the Dinnington Ridge, and on the Avest by 

 the high land above the 400-foot contour. This lake (which 

 may be called the Pont Lake), overflowing at the lowest point, 

 between East and West Heddon, would cause the Heddon 

 Slack to be cut. 



The next stage in the passing of the ice of which we have 

 evidence seems to have coincided with the retreat of the ice- 

 sheet a little eastwards, along with the temporary clearing of 

 the Dinnington Ridge, the edge of the ice resting on the north 

 side of the Ridge, and allowing the waters of the lake to 



* In Northumberland and the Northern Counties generally, the smaller valleys 

 are called cleughs, denes, hopes, slacks, nicks, gashes, and swires, the choice of name 

 depending partly upon the position and character of the valley, and pai-tly upon 

 local usage. Slack is the generic name for any surface-depression whether caused ,; 

 by running water or not, and is thus a convenient word to apply to valleys of the 

 kind described above. Swire — a word surviving in place-names, laut otherwise 

 obsolete — might well be used as a distinctive name for valleys having the character- 

 istics of the above " slacks" or "dry denes." Its use was first suggested by Lebour 

 (Geol. Mag., vol. 6, p. 443), and more recently by Woolacott (Geol. Joui\, July, 1907). 



