JOWETT AND MUFF : GLACIATION OF BRADFORD, ETC. 195 
The same year Mr. R. H. Tiddeman* adduced evidence 
from striae and drift that the Pennine watershed west of 
Skipton had been over-ridden by an ice-sheet from the 
west. 
In 1873 Russellf shortly described the character of the 
boulder-clay and gravels of the Bradford district. He 
considered that the gravel ridges extending from Burley 
Moor to Hawkes worth were eskers. 
In 1875 the Survey Memoir on the Geology of the 
Burnley CoalfieldJ described the distribution of drift on the 
western flanks of the Pennines, and mentioned the occurrence 
of a driftless area east of Boulsworth and Black Hambledon. 
To the north of Combe Hill drift was traced continuously 
across the low portion of the main Pennine ridge. In the 
gap between Combe and Crow Hills no drift was found on 
the watershed (1,125 feet), the first traces being met with 
IJ miles down the eastern side. 
Green and Russell in the " Geology of the Yorkshire 
Coalfield " (Survey Memoir, 1878), defined the margin of the 
drift-covered area as following the water-parting between 
the Aire and Calder as far as the head of the valley of the 
Bradford beck, and then passing in a general easterly 
direction through Leeds. Details of numerous occurrences 
of the superficial deposits in Airedale are given. 
In 1887 Prof. H. Carvill Lewis § stated that the Airedale 
Glacier held up two lakes on its southern margin. One of 
these occupied the valley of the Bradford Beck, the other 
the Worth Valley. 
In the " Report of the Director-General of the Geo- 
logical Survey for 1895," Mr. Tiddeman was credited with 
remarking that gravel mounds occur in Airedale at all 
elevations from 1,150 feet to the valley bottoms, and therefore 
* Quart. Joum. Geol. Soc, vol. xxviii., 1872, p. 471. 
t Brit. Assoc. Report (Bradford), 1873, Trans, of Sections, p. 88. 
X London, 1875. 
§ Brit. Assoc. Report (Manchester), 1887; also " Notes on the Glacial 
Geology of Great Britain and Ireland," London, 1894. 
