230 JOWETT AND MUFF I GLACIATION OF BRADFORD, ETC. 
a lake was impounded in the valley of Farnley Beck and its 
tributaries by the Airedale glacier, which stretched as a dam 
across the mouth of the valley from Armley to Middleton. The 
discharge of this lake would take place by the broad but steep- 
sided gap* which cuts through the watershed one mile west- 
north-west of Ardsley Station. The surface-level of the lake 
would be about 380 feet above O.D. 
The Overflow-channels oj the Harden and Cottingley Valleys. — 
The ridges bounding the Cottingley Valley are gashed through 
by a series of dry valleys, which afford some evidence of the 
oscillation of the ice-front (see PL XVI.). On the east side 
there is first a marginal channel and shallow valley at the Bogs 
on the hillside south of Chellow Dean. It commences as a 
terrace, easily distinguishable from a feature due to a hard bed 
of rock, at a point 300 yards south of Prune Park, at an altitude 
just below 850 feet, and runs in a winding course along the 
hillside eastwards to Chellow Dean. In the lower part of its 
length, from the Bogs to Chellow Dean, it becomes a shallow 
valley running obliquely across the contours and ending off in 
a steep fall on the edge of Chellow Dean. 
The second gap on the east side of the Cottingley Valley 
is Chellow Dean, which has already been described (p. 222). 
Its intake-level is 720 feet. The third channel is a dry valley 
commencing at Nailer Rough, two-thirds of a mile north-east 
of the head of Chellow Dean. It runs in an easterly direction 
across a gently- sloping plateau and falls into the head of Red 
Beck, a tributary to the Bradford Beck. It should be noted 
that its intake-level is 750 feet, i.e., higher than that of Chellow 
Dean. The fourth channel commences at Noon Nick, a little 
N. of the last, and at a level of 695 feet. Its course is very 
remarkable for the valley runs for fully a mile along the edge 
of the steep escarpment of Stony Ridge, and is in some places 
not 50 yards from the edge of it. An interesting feature occurs 
200 yards west of the point where the high road (Toller Lane) 
crosses the valley. A sudden descent takes place in the floor 
of the valley, and at the same time it widens considerably. 
*A double fault is marked on the Geological Survey Map as passing 
through this valley. 
