134 
PHYSICAL GEOGRAPHY 
'l lie southernmost portion or proper coal tract is a vast slightly 
concave surface, rising near Sheffield to the south-west, near Hud- 
dersfield to the west, and near Leeds to the north, every where ending 
upon surfaces of millstone grit and other strata associated with it 
which rise still higher, and form the summit of drainage along the 
boundary of the county. The unequally resisting materials of this 
great area have been unequally acted on by atmospheric, fluviatile, and 
diluvial agencies, so as to present ranges of hills along sandstone, 
and lines of valleys where shale prevails : and thus the whole coal 
tract of Yorkshire is agreeably diversified with a succession of in- 
tricate though continuous undulations, seldom witnessed in other coal 
countries. Great facilities are thus afforded to the discovery and 
working of coal, ironstone, flagstone, fire-clay, and other products, 
and it is probable that in no district of Great Britain have these ad- 
vantages been better understood or more vigorously prosecuted. In 
consequence the succession of strata is perhaps better known than 
in any other coalfield of equal extent, and the continuity of parti- 
cular seams of coal and layers of ironstone, for a length of thirty or 
forty miles, admits of satisfactory demonstration. 
The millstone grit rocks which are the floor of this coalfield have 
their outcrop on the hills which overhang the southern bank of the 
Wharfe from Harewood to near Skipton ; from this high point they 
return to border more closely the Aire nearly to Leeds, and rise 
again along the south side of that river by Bingley to Keighley, 
where they join themselves to the general summit of drainage which 
they follow into Derbyshire without once permitting the appearance 
of the subjacent limestone, though a considerable thickness of calci- 
ferous shales occurs below the grit in several valleys. 
From the Wharfe northwards to the Tees the millstone grit series 
is largely developed, but no portion of the superior or true coal mea- 
sures is seen in all this tract, though immediately on the north of 
the Tees, as on the south of the Wharfe, they appear in full force. 
Other thin seams of coal, however, of inferior quality, occur amongst 
