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The preference given to the slates from certain quarries as
requiring less weight for the covering of a roof of given
dimensions, depends not so much upon the specific gravity (which
varies at most from 2750 to 2800, or one part in 55) as upon the
fineness of grain, which enables it to bear splitting thinner.
All the rocks of this division effervesce more or less with
acids; they contain some calcareous spar and pyrites; but little
metallic ore, except a small quantity of galena, with green and
yellow phosphate of lead, which has been got near Staveley; and
some yellow copper ore in Skelwith.
Although little notice has hitherto been taken by authors of the
difference between the roofing slates of these three divisions,
yet a workman of moderate experience will readily distinguish
them: and I have endeavoured so to describe the peculiarities of
each, that those who may hereafter be engaged in examining
similar districts may be better enabled to compare them.
A conglomerate, composed of rounded stones of various sizes, from
the smallest gravel, to the weight of several pounds, held
together by a ferruginous, calcareous cement, forms a hill of a
parabolic shape, about 1200 feet in height, called Mell Fell; and
some lesser elevations extending to the foot of Ullswater. These
pebbles are apparently fragments of older rocks, rounded by
attrition, and must have been transported from some distance, as
their composition does not correspond with the rocks of the
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