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THE UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 
by the line of fault and may be easily traced the whole dis- 
tance. On the north this strip is bounded by the overlying 
Carboniferous Limestone, which has been very unevenly denuded 
and presents a long sinuous front to the Silurian, here rising 
into sharp escarpments as at Great Close and behind Malham 
Tarn House, and there receding in long gentle slopes as on 
Chapel Fell, Knowe Tell, and about West Side House. In 
a line across by Neals Ing and Cattrigg the Silurian is nearly 
two miles wdde, half a mile west of Capon Hall it narrows to 
zero, widens to about a mile at Malham Tarn, and narrows 
again to where it disappears eastwards near Gordale Beck. 
The area under consideration is included in a line drawn 
from near Capon Hall on the west, Knowe Fell on the 
southerly side of Fountains Fell on the north, round by Middle 
House and East Great Close (under Hard Flask) to High Stoney 
Bank on the east, and Kirkby Malham in the Aire Valley on 
the south. This area forms the upper watershed of the River 
Aire. 
What happens is this. All the rainfall on the limestone 
on the north side of the Silurian, and several springs which rise 
up the slopes of Knowe Fell towards Gentleman's Gate and 
Fountains Fell, sink into the limestone and are brought to the 
surface again at the edge of the Silurian rocks which are tilted 
at a high angle. These waters flow across the Silurian rocks, 
either in streams or through Malham Tarn, only to sink again 
on reaching the limestone on the south side. 
To this rule Gordale Beck has been regarded hitherto as 
the only exception, but it now transpires that Gordale stream is 
only partially an exception, and is itself undergoing absorption 
into the limestone. These waters, sinking south of the North 
Craven Fault, reappear below the great escarpments about Malham 
and Gordale formed by the Mid Craven Fault, with all the rain- 
fall and springs on the limestone area lying between the two 
lines of fault. The limestone on the south side of the Silurian 
absorbs all surface waters just as it does on the north side. 
