JOWETT AND MUFF : GLACIATION OF BRADFORD, ETC. 247 
oiily be considered as a product of atmospheric weathering, 
wliilst the more sandy nature of the drift at higher levels is due 
to the larger proportion of local detritus which it contains. 
The ice flowed down Airedale from the comparatively open 
country to the nortli-west of Skipton. Its upper layers, when 
they impinged against the hills, may therefore be expected to 
have borne a smaller quantity of stones and mud than the lower 
layers constantly moving over the surface of the ground. 
The easterly termination of the glacier has not been fixed. 
If, as is possible, it entered Lake Humber.* its termination may 
well be indefinite. Terminal moraines, however, which accumu- 
hited during halts in the general retreat occur in the main valley. 
They lie in the more constricted portions of the valley. 
The hills south and west of Airedale, although reaching to 
a height of 1.700 feet in Boulsworth. were not over-run b}'' the 
ice. and \vere probably free from snow in summer. At any 
rate the snow was sufficiently melted off them to prevent the 
formation of local glaciers. It seems that tlie snow-line in 
Airedale during the Glacial Period cannot have been below 
1,500 feet, and was ])erliaps more than 1.700 feet above Ordnance 
Datum. 
A large ])ortion of tlie work, of which this paper is a record, 
was carried on whilst the authors were closely in touch with 
Prof. Kendall, whom the\' desire to thank for his generous 
help. In particular. Prof. Kendall's work on similar problems 
in Cleveland has thrown a flood of light upon the interpreta- 
tion of the diy valleys in Airedale. 
We also thank Mr. Godfrey Bingley for the photograph 
from which PL XX. is reproduced. 
* P. F. Kendall. Q.J.G.S., vol. Iviii., 1902, p. 567. 
