DAVIS: SOURCE OF BOULDERS IX CALDER VALLEY. 143 
and even in some few instances with rocks of Scotch 
derivation, whilst the flints are similar to those occurring in 
the Chalk in the eastern parts of the Yorkshire Wolds. 
There is an entire absence of shells of Mollusca, but near 
Thornhill the trunks of several trees have been found at a 
few feet below the surface of the gravel beds presenting an 
appearance indicating that they grew at no great distance 
from the position they occupied when found. A more 
detailed description may be found in the Proceedings of the 
Yorkshire Geological and Polytechnic Society for the year 
1875, page 93.* 
In addition to the boulders already enumerated, Shap 
Fell granite has been found in the district south-east of 
Wakefield. Though comparatively rare, they are found 
sufficiently often to form a characteristic boulder ; the large 
masses of pink felspar being a very important constituent, 
which renders their identification unmistakable. The 
occurrence of this granite, as will be shown hereafter, 
throws a most important light on the origin of the gravels. 
The question at issue is, "How were the erratic boulders 
transported into the Valley of the Calder?" There are two 
sources from which the boulders may have been derived, the 
one on the western side of the Pennine range of hills 
dividing Lancashire and Yorkshire, and the other occupying 
a part of the great plain of the Ouse in the central part of 
Yorkshire. In all probability the glacial clays, originally 
containing the boulders, may have had a common origin in 
the mountainous ranges of Westmoreland, or possibly amongst 
the mountains of the south of Scotland. Whether one or 
both these localities served as the source of the glacier, it 
appears to have passed along the valley of the Eden, 
grinding against the Crossfell escarpment until it reached 
* See also a paper by J. Travis Clay. Esq., of Kastrick, Proc. Geol. and 
Polyt. Soc. of the West Biding of Yorkshire, vol. i. p. 201 (1841). 
