92 THE GLACIAL PHENOMENA OF THE COUNTRY 



similar to those about to be described, and referred their 

 formation to ice agency at the close of the Glacial Period. 



These old water-courses are in the nature of long, clean-cut 

 valleys or slacks with parallel banks and well-defined wind- 

 ings. Sometimes they cut through rock, at other times through 

 drift, or occasionally partly through both. Where the banks 

 are rocky, they are steepest on the convex sides of the wind- 

 ings. The bottoms are flat and of uniform slope, and covered 

 with a rank growth or peat. The slacks are often quite dry; 

 sometimes they contain a small burn, sike, or letch, which 

 bears no just proportion to the depth of the slack or the size 

 of the. windings ; they generally cut the watersheds between 

 large adjacent valleys. There can be no manner of doubt 

 that they are the deserted channels of short-lived, fair-sized 

 streams, and the survival of a coarse pebble-bed in one of 

 them completely confirms this view. 



In the district under discussion seven of these slacks have 

 been discovered and investigated. The Whalton Ridge is 

 breached near Edington by one of them, which I shall call the 

 Shilvington Slack. It takes in at 345 feet, and is traceable as 

 a strong feature as far almost as Broad Law, a distance of i^ 

 miles, where it mouths at 260 feet. A small stream, the 

 Shilvington Burn, enters it near its head; the slack is cut 

 through rock, slightly capped in places with drift, and is of 

 especial interest in that it is, apparently, the only one connect- 

 ing the valleys of the Wansbeck and Blyth ; and furthermore 

 it bears on one of its banks the coarse pebble-bed mentioned 

 above, as witness to the stream which produced it. 



The lofty watershed between the Tyne and the Pont and 

 Blyth (the Dinnington Ridge) is breached by four slacks in 

 "parallel sequence"; these may be referred to as the Heddon, 

 the Callerton, the Luddick, and the Woolsington Slacks, 

 naming them in order from west to east. The first and most 

 westerly is a deep gorge cutting chiefly through rock between 

 East and West Heddon. The Dewley Burn enters it near its 

 head, but is there a quite insignificant stream. 



