CARTER : THE EVOLUTION OF THE DON RIVER-SYSTEM. 405 
This supposition demands a considerable extension west- 
wards of the Hickleton escarpment of the Magnesian Limestone 
in order to provide a satisfactory watershed separating the Dearne 
from the Dove in pre-glacial times. The way in which the 
Magnesian Limestone pushes out shallow spurs over the Middle 
Coal Measures near Hickleton suggests that this was the case 
(Fig. 6), and the base of the Permian at Hickleton is no less than 
340 feet above O.D. Drawing a line westwards from Hickleton 
to Darfield, the level of the shales and soft sandstones gradually 
declines to 150 feet above O.D. at Thumscoe Hall, and when 
the post-glacial valley of Thumscoe Dike is crossed, the contour 
of 175 feet is quickly reached at Billingley. Thus it does not 
seem impossible that a low watershed of shales and soft sand- 
Fig. 7. 
SECTION ACROSS THE HAMPOLE GORGE IN THE MAGNESIAN' LIMESTONE. 
(This Section was made on the same scale and for comparison with the Don and 
Balby Section, Fig. 4 in " The Glaciation of the Don and Dearne Valleys.) 
stones, say up to 250 feet, possibly capped by a thin limestone 
bed, may have been all that the glacier moving southwards 
through Frickley valley had to meet. In my paper on the 
glaciation of this area* I have tried to show how the oncoming 
of this glacier would account for the gorge of the Dearne at 
Darfield and for the erratic course of Thurnscoe Dike. 
VI. — The Rother. 
In considering the Rother one finds a river of considerable 
complexity, which exhibits some curious features (Fig. 8). The 
main channel of the modern Rother south of Woodhouse and 
its direct continuation, the Doe Lea, form a subsequent stream 
* See p. 427. 
