CARTER : THE EVOLUTION OF THE DON RIVER-SYSTEM. 401 
and Lower Coal Measures, and unhindered by the WharncUffe 
Grit, which thins out rapidly westwards as well as southwards, 
would soon lengthen its course, and ultimately capture the 
head waters of the Penistone Don above Langsett, leaving the 
col at the Flouch Inn (Fig. 2). The main stream would at the 
same time continue its cutting work backwards along the course 
of the Wortley until it captured the Don at Penistone, and 
enabled Scout Dike in its turn to work back and capture Broad- 
stone Beck, leaving the Cawthorne stream and the Dove as 
beheaded remnants (Fig. 5). This would complete the evolution 
of the form of the Upper Don, which since then has been occupied 
with establishing itself more and more deeply in its new channel. 
V. — The Dearne. 
Turning now to the Dearne, we find north of Ingbirchworth 
that the Penistone Flags bend round to the north-east and east, 
and two strike streams flowing along Denby Dale and from 
Shelley (PI. LIII.), along the junction of the Lower and Middle 
Coal Measures, unite to form the Bretton stream. This stream 
makes a sharp south-easterly bend at Haigh, where it faces 
the escarpment of WooUey Edge, and, flowing on by Darton, 
receives the Cawthorne stream. The strike of the Middle Coal 
Measures at Woolley Edge bends round to the south-east, and 
the Bretton stream follows the strike, changing from a dip to 
a strike river. This suggests that the Darton branch of this 
stream is a subsequent which captured the Bretton stream 
at an early date, probably before the capture of the Penistone 
Don, as there is no mark of a channel or dip at the part of Woolley 
Edge at which one would expect it. The Cawthorne stream, 
which appears to be the original strike river which captured 
the Bretton, flows across the Middle Coal Measures in an easterly 
direction, cutting through the Woolley Edge, Oaks, Lower, 
Middle, and Upper Che vet Rocks (Fig. 6), and then makes 
a rectangular bend to the south at Great Houghton, turning 
away from the escarpment of the Great Houghton Rock, and 
becoming a strike river, which passes along the edge of the 
Upper Che vet Rock as far as Darfleld, where it bends round 
again, crosses the Upper Chevet Rock backwards, in a narrow, 
