CARTER : THE EVOLUTION OF THE DON RIVER-SYSTEM. 407 
running through the Middle Coal Measures, roughly parallel 
to the Magnesian Limestone escarpment, which it has denuded 
into a fairly straight ridge. Parallel to the Doe Lea, and separ- 
ated from it by the Brimington anticlinal of Lower Coal Measures, 
is another subsequent stream, which has worked its way back- 
wards along the strike of the Middle Coal Measures southwards 
to Clay Cross. 
These streams are united by a dip stream. Barlow Brook, 
which rises in the Lower Coal Measures of Ransley Moor and 
Car Top, receives the River Drone, and flows directly east to 
Staveley. Here it makes a curious double rectangular bend to 
the north and east, and falls into the Doe Lea near Renishaw. 
Flowing down from the edge of the Magnesian Limestone escarp- 
ment at Clowne, towards Seymour Colliery, is a stream the 
course of which suggests that it is the obsequent from Barlow 
Brook, after capture by the subsequent Rother ; and at Clowne, 
though there is no gap in the ridge, the head waters of the Poulter 
rise almost at the edge of the escarpment, and may represent 
a beheaded remnant. Following out these suggestions, the 
easiest way of explaining this curious physical structure appears 
to be to assume that Barlow Brook is the chief consequent of 
this district, and that originally it flowed eastwards over the 
Permian ridge. Also that the Doe Lea and the Chesterfield branch 
of the Rother are subsequents which have worked back each 
along the strike of a belt of Middle Coal Measures. When 
Barlow Brook was captured by the Rother, the Poulter was 
left as the beheaded remnant. 
At Kiveton the Magnesian Limestone is traversed by a 
gorge (Fig. 8 and PI. LIIT.) commencing at the 300-foot contour 
at the western end, through which a little stream runs, which 
rises at Harthill on Middle Coal Measures, makes a rectangular 
bend as it enters the gorge and flows through it into the Ryton. 
Directly west of the entrance to the gorge there is a circular 
patch of higher ground, called Wales, rising to the 400-foot 
contour, with a dip in the contour on each side of it to 330 feet 
(PI. LIV.). From the more northerly of these cols a stream 
flows back into the Rother, and the canal has diverted a similar 
small stream from the southward col. 
