224 JOWETT AND MUFF : GLACIATION OF BRADFORD, ETC. 
Wibsey Bank Foot discharged by the gap which cuts through 
the watershed at the last-named place. Traced from the west- 
ward the watershed on the south side of the Bradford br.sin 
nowhere falls below 800 feet until Wibsey is reached. At 
Wibsey Bank Foot the summit of the ridge separating the Brad- 
ford basin (Airedale) from the Spen Valley (Calderdale) drops 
sharply to 670 feet, and continues at about that altitude, or 
a slightly lower one for some distance eastwards. Just at the 
foot of the steep slope, the watershed is cut through from north- 
west to south-east by a streamless valley which is about 25 feet 
deep on the watershed. Followed to the south-east the valley 
is found to deepen and broaden. Traced to the north-west it 
shallows after passing through the natural watershed. Its 
north-eastern side almost disappears, but a shallow depression 
or a terrace at the foot of a steep scarp is continued for a mile 
to Close Top Farm, above Great Horton, where it reaches an 
altitude of 700 feet above O.D. Thus, at the furthest extension 
of the ice which we have been able to trace, the surface-level of 
the Bradford Lake must have been at a height of 700 feet above 
O.D. The surplus water running from near Close Top Farm 
to the watershed formed, or at least greatly intensified the scarp 
feature described above, and commenced to cut the gap through 
the watershed at Wibsey Bank Foot. When the ice-front moved 
back a little, the overflow took place directly into the gap at 
Wibsey Bank Foot, and the level of the lake sank to 660 feet. 
The cols on the watershed west of W^ibsey Bank Foot are 
not gashed through by valleys. They present the ordinary 
features of cols and may be described as saddle-shaped. The 
evidence also from the glacial deposits does not suggest that the 
ice ever reached up high enough to turn the overflow of the 
Bradford Lake over them. The same remarks apply to the 
broad pass, just over 1,000 feet above O.D., which leads from 
Thornton into the Harden Valley, but the col to the north of 
Thornton Heights is different. The watershed is at Stream 
Head Farm, whence a tiny stream flows towards the Bradford 
basin in a flat and fairly open valley for a third of a mile. The 
valley then closes in and the stream enters Bell Dean, a narrow 
gorge over 100 feet deep and a quarter of a mile long. The 
