105 
the most part by a thin coat of rain- wash and soil, as at the 
section in Eipley Fields ; but beneath Manchester Eoad we 
have 25 feet of upper boulder-clay which, as it thins out, 
overlaps the upper till near Bowling Back Lane. It is a 
yellow clay with white partings, full of angular fragments of 
flagstone, shale, and coal — rarely ice-scratched — all derived 
from the parent rocks in situ : no rock foreign to the basin is 
to be found imbedded therein. This upper boulder-clay is 
moderately developed along the eastern brim of the basin, 
and is continuous to and bej^ond Leeds, always retaining its 
strictly local character. 
Another blue- clay found in this neighbourhood presents 
some peculiarities deserving special notice. It occurs within 
a short distance of the upper altered till, but on the east side 
of the watershed, 600 feet high. It ranges from Quarry Gap 
across Calverley Moor to Eccleshill and Idle, that is, outside 
the Bradford drainage area. It is largely worked by Messrs. 
Cliff, at Thornbury, and a good section is obtained where 
the Idle Railway passes under the Leeds and Bradford turn- 
pike road. It is a stiff tenacious clay, difficult to work. Its 
upper portion carries numerous large angular or sub-angular 
blocks of grit and sandstone, of from 10 to 30 cubic feet 
dimensions. Occasionally, lenticular patches and streaks of 
dark sand and fine gravel are exposed, such as one would ex- 
pect to find in the moraine profonde of a glacier ; while the 
close texture of the clay must be due to the heavy pressure 
of a sheet of ice. The blue clay represented by this section 
resembles so closely, in general appearance, the altered till, 
as to be known among the local excavators by the same name 
(Bowling tough), and both clays have been grouped together 
by previous observers.* But the essential difference between 
* T. P. Teale, Brit. Assoc. Reports, 1858. D, Mackintosh, Geo. and Poly. 
See. Report, 1870. 
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