758 REPORT— 1900. 



phase, a Ic le of ice actually stood over the broad depression in the watershed there, 

 and smeartd over the low slope a thin cover of boulder clay which entirely obli- 

 terated the pre-existing minor surface features. 



The presence of drift brings the ice-eilge far up the slope as we follow the 

 watershed round past Bowling to Laiaterdyke, where the ice laid down in a hollow 

 in the solid rock, outside the Bradford Valloy, a mass of clay 70 feet in thickness. 

 The country east of Tyersal is driftless, but the ice passed over the ridge from 

 Undercliffe to Wrose Hill, boulder clay occurring on the top of Stonehall Hill, 

 Eccleshill, at an altitude of 700 feet, and also all along the eastern slope of the ridge. 

 The altitude gradually drops as far as Newlay, where a mass of gravel 30 feet 

 thick occurs at 200 feet O.D., and 75 feet above the level of the river. All the 

 pebbles are rounded, and though limestones are numerous, they are small in size, 

 rarely exceeding four inches in diameter. Tins gravel marks the last definite trace 

 that we have found in .\iredale of the Airedale ice. 



From similar evidence to tliat which we have adduced in the case of Airedale, 

 we conclude that there was a glacier in Whavfedale which was confluent with the 

 Airedale Glacier to the N.W., and also to the S.E. of Rumbles Moor, leaving 

 only its highest ridge uncovered as a ' nunatak.' The limiting altitude of the ice 

 on the west is 1,250 feet, sinking gradually to about 1,100 feet on the east. The 

 configuration of the country, and the presence of a series of drift ridges running 

 continuously from Wharfedale on the N.W. to Airedale on the S.E., lead us to 

 believe that the Wharfedale Glacier pushed in as far as Guiseley, the onset of the 

 Airedale Glacier having been considerably weakened here by its passage over 

 Hope Hill and the iiigh ground between Hope Hill and Rumbles Moor. The 

 outermost of these lidges consists largely of gravel containiug limestones, and runs 

 from Lanshaw Delves, on llkley Moor, to Hawkswortli. 



Over the districts of Guiseley, Yeadon, and Horsforth, drift occurs sporadic- 

 ally, and we have been unable to draw a boundary line between the Airedale and 

 the Wharfedale ice in this region. 



The striae indicate a general ice-movement from the N.W. Those which we 

 have observed at higher levels are more strictly parallel to this general direction, 

 whilst the others more nearly conform with tlie trend ot the particular part of the 

 valley in which they occur. A greater freedom of movement would be expected 

 in the upper layers of a glacier than in the lower layers, which must mould them- 

 selves to tJie inequalities of the glacier bed. 



The whole area, within the limits traced out above, displays abundant 

 evidences of the characteristic remains of a glacier. From Apperley Bridge 

 upwards the lower portion of the main valley is full of moraine mounds left behind 

 during the retreat of the ice. The best examples are at Tong Park, near Esholt ; 

 Nab Wood, near Saltaire ; and Bingley. 



4. The Extra- Glacial Drainage. 



Every embayment in the unglaciated area— at the edge of the ice at its 

 greatest extension, and during the various phases of retreit — would, by receiving 

 the natural drainage, be converted temporarily into a lake. The level of each 

 lake would be determined by the height of the ice-barrier and of the watershed 

 around the margin of the lake. The height of the ice-barrier becomes gradually 

 lower from N.W. to S.E., and hence we should expect the level of each succeeding 

 lake at some particular phase to be lower than that of the lake preceding it to 

 the N.W., so long as the drainage water is confined on that side of the main 

 watershed proximal to the ice. 



We should therefore expect an overflow of the waters of each lake, by the 

 lowest point in its margin, into the succeeding lake at the period of greatest exten- 

 sion of the ice and at every other temporary stationary period during the general 

 recession. 



The peculiar spur-cutting valleys above mentioned we believe to have been 

 the overflow-channels of such lakes. Typically, they are flat-bottomed, steep- 

 sided grooves passing completely through the watershed, characters indicating 

 rapid cutting by considerable volumes of water. They often end quite suddenly 



