394 CARTER : THE EVOLUTION OF THE DON RIVER- SYSTEM. 
in question. Thus Broadstone Beck flows eastwards to Ing- 
birchwortli (Fig. 2), and just on the 750-foot contour bends to 
the south-east. Directly opposite to it at this bend is a dip 
of the contour of the opposing watershed to 750 feet, which the 
stream avoids, cutting its channel southwards, as Scout Dike, 
through the higher land at Hoy land Swaine. Just over the 
watershed at Ingbirchworth rise the head waters of Daking 
Brook, which flows by Cawthorne into the Dearne. Again, the 
Don at Penistone faces a dip to 730 feet in the eastward ridge, 
between the 800 foot contours of Hoyland Swaine and Thurgo- 
land, and on the other side of this ridge the Dove takes its rise, 
continuing the line of the Upper Don eastwards. Turning 
away, however, from this col southwards, the Don strikes into 
the elevated plateau of Wortley, which rises in several places 
to more than 1,000 feet on either bank. It is obvious that in 
order to cut through a ridge of 1,000 feet water must have flowed 
at that elevation when this work of denudation commenced. 
But no reconstruction of the physical geography will permit us 
to assume a barrier from Wortley to Hoyland Swaine of such 
a height as to compel the waters of the Don to take this southern 
course. We must therefore seek for a more satisfactory ex- 
planation, and that of river capture is the most feasible. This 
teaches us that a stream flowing southwards from the Wharn- 
cliffe watershed cut its way back through that ridge, tapped 
the streams of the Don and Broadstone Beck successively at 
Penistone and Ingbirchworth, and drew their upper waters 
down by its steep channel through the Wharncliffe gorge to 
the Sheaf at Sheffield, and left the Dove and Daking Brook as 
beheaded remnants to flow eastwards from the edge of the new 
ridge which was produced gradually by the deepening of the 
new valley of the Don. 
Usually after passing in a fairly straight course through 
a mountain gorge a river on debouching into a plain at once, 
its velocity being checked, begins to migrate in wide loops, to 
and fro in the flat land. The opposite to this happens in the 
case of the Don. It flows south-eastwards in a straight course 
from Penistone to Thurgoland in a V-shaped valley, but on 
entering the gorge through the Wharncliffe plateau, it suddenly 
