CARTER : THE EVOLUTION OF THE DON RIVER-SYSTEM. 403 
deep gorge, and falls into the valley of the Dove. A short 
distance to the east of the Dearne at Darfield is a little beck, 
Thurnscoe Dike, which takes its rise in the shales between the 
Great Houghton and the Houghton Common Rocks, flows first 
as a strike stream, and then, crossing the end of the deserted 
valley which passes north of Bolton- on -Dearne, swings back 
parallel to the Darfield Gorge, and crosses the Upper Chevet 
Rock into the valley of the Dove at Carr Head (Fig. 6). 
That these streams should turn away from the wide open 
country in front of them, and especially from open valleys like 
that of Little Houghton and Bolton-on-Dearne, without some 
very powerful compulsion, seems incomprehensible, and in my 
paper on the glaciation of this area* I have tried to show how 
the advance of a glacier from the north through Frickley Gorge 
would effect tliese curious diversions. I suggest as probable 
that the Dearne, which is a dip river as far as Little Houghton, 
crossing the WooUey Edge, Oaks, Lower, Middle, and Upper 
Chevet Rocks (Fig. 6), in pre-glacial times flowed on along a 
normal dip course, cutting through the Great Houghton Rock 
at Thurnscoe and the Houghton Common Rock at Frickley 
(200 feet). The deserted valley at Frickley between Clayton 
and the Magnesian Limestone escarpment at Hickleton, has the 
appearance of an old river valley of considerable antiquity, the 
centre of which, at the 200-foot contour, is quite streamless, and 
the sides rise in a mile on either hand, at Clayton and Hickleton, 
to the 300-foot contour, and then slope upwards to 385 feet 
and 362 feet respectively above O.D. This gorge opens out 
northwards into a wide valley, drained by several little dikes 
which unite in a small stream which flows through the Mag- 
nesian Limestone by the old gorge of Hampole (PI. LIIL). This 
gorge, which is comparable with that of the Don in importance, 
appears to require a much more considerable river to explain 
it than the small stream which it now conveys (Fig. 7). 
I venture to suggest that the Dearne in pre-glacial times, after 
flowing through Frickley Gorge, found its way through the 
Permian escarpment into the Triassic plain by Hampole Gorge 
(Fig. 5). 
* See p. 427. 
