CARTER : GLACIATION OF DON AND DEARNE VALLEYS. 435 
would gradually creep up to Mirfield, accounting for the great 
deposits of drift at 150 feet above O.D., with abundance of 
great angular blocks of ganister, and to Ell and, where there 
are extensive detrital deposits in the valley, and up to Mytholm- 
royd, where it would account for the great delta from 330 to 
360 feet above O.D.* The northern edge of this lake would 
creep up to and over the watershed of the Calder and Aire at 
Lofthouse and Rothwell, would discharge its waters over the 
gap at Tingley into the Churwell valley, and, lapping round 
Middleton, would be bounded northwards by the Airedale 
glacier, t This lake would thus serve to explain the Rothwell 
and Oulton sands and gravels which cap the watershed between 
the Aire and the Calder from the 175th to the 275th contour. 
These gravels are largely composed of Coal Pleasure material, 
but pebbles of Carboniferous Limestone, chert, and Silurian 
grit have also been found in fair numbers. J I regard these 
detrital deposits, often well bedded and associated with fine 
tenacious clays, as part of the lateral moraine of the Airedale 
glacier rearranged in the lake which washed the side o*' the glacier. 
The termination of the expansion of Lake Calder would be reached 
when it reached the level of the col between Crigglestone and 
West Bretton (405 feet above O.D.), when its waters would then 
be discharged into Lake Don, by way of which they would pass 
by the Kiveton gorge into the Triassic plain, which was then 
probably also a glacier lake. 
The author does not contend that the evidence now adduced 
amounts to a demonstration, but the considerable number of 
facts brought forward appear to him when linked together 
to form a powerful chain of argument. When the re -survey of 
this area is undertaken by the Geological Survey, it is 
probable that many additional facts viill be unearthed by 
which the results of this investigation will be tested. All that 
* Law and Simpson, Report on the Drift Deposits of Mytholmroyd, 
Proc. Yorks. Geol. and Polytec. Soc, XIV., p. 231. 
t Jowett and Muff, Glaciation of Bradford, &c., Proc. Yorks. Geol. 
and Polytec. Soc, XV., 245. 
^E. Hawkesworth, Programme for the Leeds Meeting, Y.G. and P.S., 
March 2nd, 1905. 
k 
