178 
WILLIAM SMITH : HIS MAPS AND MEMOIRS 
" That there are such opposite lateral rises and dips in the strata, 
where the coal-measures are deeply unconformably covered by the red 
marl, is well known in the extensively wrought colleries of Somersetshire 
(where I commenced my studies of geology) ; the planes of the coal are 
subject to hollows and ridges, though the extent of these irregularities 
may not yet be known. 
" We see that the strata, in part, or in the whole series of strata in 
their superficial exposures, form such natural hollows and ridges to a 
great extent, chiefly across the bearings of their ranges ; and, therefore, 
we have a right to expect such forms in them even where they are deeply 
covered. 
"The broad and very long coalfield of South Wales terminates north 
and south with opposite rises in the strata. 
" The coal in Durham rises, in its southward boundary, nearer to 
the surface ; so that good coal is found at no great depth beneath its 
uncomformable cover of magnesian limestone. 
The northernmost coal of Yorkshire rises northward beneath a cover 
of the same limestone, and ranges E. and W. : forming, with its south 
western boundary, a westerly pointed figure, widening and deepening 
south-eastward. 
" The question of an east or north-easterly continuation of the coal- 
measures can only be entertained at the easterly end of the east and 
west range, before mentioned ; but we mast previously turn to other 
places, to see, by analogy, how far any subterraneous deflection in the 
range of the coal-measures may be thereabout expected. 
" Along the westerly edge of the coal-measures, both in Yorkshire 
and Derbyshire, there are well known irregularities occasioned by 
elevations and depressions across the general range of the series, causing 
sinuosities in the marginal edges of the coal-fields. The lands eastward, 
over the ridges, contract, and those westward, in the hollows, expand 
the width of the coal-measures ; so that the first rise in the north side of 
the Dun causes a vacant space between Sheffield and Chapletown ; and 
the second rise south of Sheffield, and in Derbyshire, causes a vacant 
space in the productive coal-measures between the high part of Sheffield 
Park and Coal Aston ; and in the hollow between these two ridges the 
coal is thrown back under Sheffield. But there is a greater westward 
receding in the Dronfield trough, one side of which rising to the north 
causes a long east and west range through Coal Aston. 
