392 CARTER : THE EVOLUTION OF THE DON RIVER-SYSTEM. 
capture (L, K) are called beheaded remnants, and any stream (M) 
flowing back along the old bed from the escarpment into the 
capturing river is called an ohsequent stream. 
In glacial diversion the normal drainage is obstructed by 
an advancing ice-front, and a lake is formed, the overflow from 
which cuts a new channel across the lowest part of the enclosing 
watershed. This channel, if only occupied for a comparatively 
short period, may be deserted on the retreat of the ice-barrier, 
and the stream will then return to its old channel, unless that 
is obstructed by morainic deposits, when the overflow from the 
diminished lake will cut a new channel across or at the side 
of the moraine. ' If the glacial obstruction persist for a period 
sufficiently long to allow of the drainage overflow cutting down 
its channel below the contour of the original stream bed, or 
below the level of the moraine if the old valley be obstructed, 
the removal of the ice-barrier will not influence the course of 
the stream, which will continue to follow the new gorge, and 
establish itself as the main river-channel. 
III. — The Upper Don. 
In considering the Upper Don by the help of the foregoing 
principles of river capture, it is evident that the upper portions 
of two of the streams (Broadstone Beck and the Don above 
Penistone) partake of the character of consequents, i.e., they flow 
eastwards dowTi the slope of the Pennine arch and across the 
dip of the strata. On the far slope of the opposing low watershed, 
on each side of the higher land of Hoyland Swaine, streams are 
found also running eastwards, and giving a strong suggestion of 
ancient continuity of flow. These latter streams are interpreted 
by the author as the beheaded remnants of the consequents 
in question. 
The eastern retaining watershed of the Don below Penistone 
(PI. LIII.) is evidently a continuation northwards of the plateau 
of Wharncliffe Chase, a great portion of which is above the 
800-foot contour. In this watershed there are outlying patches 
of land above this contour (800 feet) at Thurgoland and Hoyland 
Swaine, but the intermediate parts of the ridge have been lowered 
by denuding agencies to form a col opposite each of the streams 
