GILLIGAN : ALLUVIAL DEPOSITS AT WOODLESFORD, ETC. 271 
Evidently then, the Vale of York ice, which I have shown probably 
contributed the boulder clay, must have incorporated a large amount of 
material from the Millstone Grit, and the lesser quantity of monazite 
is quite in agreement with the fact that the Rough Rock was not so 
important a contributor to the burden borne along by this Vale ox 
York ice, for the Rough Rock does not occur to the north, and it is 
the bed from which the greatest quantity of monazite has been obtained 
in my work upon the heavy minerals of the Millstone Grit. 
Here, then, is a direct connection between the three types of deposit 
which may be helpful in elucidating some of the problems of the 
distribution of such deposits over such an area as the Vale of York. 
For instance, if quantitative work along such lines were carried out 
for a number of boulder clays and morainic material, and the thickness 
and area of the laminated clay over the Vale of York ascertained, it 
seems to me it would be possible to obtain the volume of the original 
material which must have been redistributed in order to yield it. A 
microscopical examination of the upper laminated clay of Woodlesford 
shows that it consists very largely of rock flour, being, in fact, a very 
finely divided quartz mud, and it would thus seem to be due to the 
grinding of fresh rock in Glacial times rather than to the old soils, 
residual earths and clayey material resulting from subaerial decay of 
the rock in pre-Glacial times. In the lower laminated clay at AVoodles- 
ford there is not so much rock flour and more clayey material, and 
doubtless differences of this kind would be found in whatever clays were 
examined, resulting from a sorting of the finer clay particles from the 
rock flour the further the area of deposition may be from the source 
of supply. 
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