CARTER : GLACIATION OF DON AND DEARNE VALLEYS. 427 
This tongue of ice would dam back the Dearne at Frickley 
gorge,* causing the formation of a lake at Thurnscoe (Fig. 6), 
which appears to have overflowed along the northern edge of 
the outcrop of the Upper Chevet Rock, and excavated the valley 
to the north of Bolton-on-Dearne, falling into the Dove at 
Adwick. t A slight advance seems to have closed the Bolton valley, 
and caused the lake to overflow and cut a notch through the 
Upper Chevet Rock at Carr Head. A further advance was checked 
by the higher land at Darfield (Fig. 7), and the waters of the 
Fig. 6. 
DIAGRAM OF THE ICE-FRONT WHEN' THE BOLTOy-ON-DEARNE AND CARR HEAD 
CHANNELS WERE FORMED. 
Dearne, forming a lake reaching up to Ardsley and Barnsley, weie 
probably reinforced by the diverted drainage of the Calder, which 
would escape over the low watershed at Xotton (PI. LXI.). Thus 
there would be a considerable current of water available for the 
cutting of Darfield gorge, which has every sign of comparatively 
* See previous paper, p. 403. 
t See also Fig. 6, p. 404 
