JOWETT AND MUFF : GLACIATION OF BRADFORD, ETC. 225 
Dean opens rather suddenly at its lower end into the head of 
the broad and open valley of Pitty Beck. The altitude of the 
col at Stream Head is 870 feet, that of the lip of the gorge at 
Bell Dean 900 feet. It is obvious from the conformation of the 
ground that the ridge through which Bell Dean is cut was at 
at one time the watershed between the Bradford and Harden 
Valleys. 
It has already been shown that at the time of the greatest 
extension of the Airedale glacier, its margin abutted against 
Harrop Edge immediately to the north of Stream Head Farm. 
The waters thus impounded at the head of the Harden basin 
discharged into the Bradford basin and gradually cut down Bell 
Dean. The level of this lake therefore was at first 900 feet, but 
by the cutting back of the watershed to Stream Head it was 
gradually reduced to 870 feet. 
Where the waters discharging through Bell Dean would enter 
the Bradford Lake, viz., near the junction of Pitty Beck with 
the main stream flowing from Thornton, there is a delta of 
stratified gravel and silt. It is roughly triangular in shape, 
and the apex points up the valley of Pitty Beck. A section 
near Leventhorpe Mill is — 
Current -bedded gravel and sand. . about 20 feet. 
Micaceous laminated clay . . . . . . 5 feet. 
Blue boulder-clay . . . . . . . . . . 25 feet. + 
The gravel consists chiefly of water-worn pebbles of sandstone 
and flakes of shale, similar in character to the rocks in which 
Bell Dean is eroded. There were also noted a few pebbles of 
Millstone Grit, chert, decomposing Carboniferous Limestone, and 
water-worn pieces of coal. The sand is largely made up of 
particles of shale, so that it is of no use for a building sand. The 
current-bedding is very marked. It dips at an angle of about 
30° away from Bell Dean (see PI. XVIIL, Fig. 1). The gravel 
forms a gently-inchned surface at two levels, viz., 625-600 feet 
and 575-530 feet. Xear Leventhorpe Hall there is a distinct 
drop from one to the other. Neither of these levels corresponds 
with the level of the Bradford Lake at its greatest height. 
That much of the delta has not been deposited in its present 
position during the maximum extension of the ice is evident 
o 
