104 
glacially weathered rocks lying on the slopes of the valley 
and in the bed of the river may have furnished many of the 
angular and round stones included in this portion of the till. 
The looser texture of the upper till may be the result of long- 
continued atmospheric influences. Air will percolate where 
water cannot pass, and the eroded surface within the till may 
mark the depth to which these atmospheric forces have pene- 
trated since the final retreat of the ice. 
That the ice-sheet travelled in the direction thus indi- 
cated by the contained rocks, is in harmony with the conclu- 
sions arrived at by those who have investigated the memorials 
of the Ice-age west of the Pennine watershed. Mr. Tiddeman* 
has demonstrated that a sheet of ice, eight miles broad and 
750 feet deep, arising north of the Craven faults, crept along 
the Ribble valley parallel to the watershed for some consider- 
able distance. The rock striae left beneath the hillocks of 
drift in the neighbourhood of Hellifield take a direct easterly 
course across the watershed, and through this depression in 
the Pennine range — only 700 feet above the sea — a portion 
of the Ribble ice was discharged, and descended the valley of 
the Aire to the plain of York ; where its course may have 
been deflected southwards by the York vale ice- stream, and 
so have given rise to the outlying patch of blue till occurring 
near Barnsley, as recorded by Professor Green. 
No marine remains have been detected in the Bradford 
till. Mr. H. B. Brady, F.R.S., has kindly submitted to 
microscopic investigation specimens of the lower and upper 
till, and writes : — " The only evidence they yield is negative. 
Both are entirely azoic ; neither contains a trace of animal 
remains great or small, and therefore palaeontological evidence 
is not forthcoming to settle the vexed question.'' 
The upper till within the Bradford basin is protected for 
* Quar. Jour. Geol. Soc. XXVIII. 477. 
