C.—GEOLOGY 75 
within a mile. The back slope to the Chesterfield syncline starts immedi- 
ately, and, though not so high, is similarly steep. By sudden change of 
pitch and oblique cross-faulting, 600 ft. of crest elevation is lost at Hasland, 
and about Heath the hogsback becomes a terrace. Southwards the crest 
picks up in the 500 ft. high, mile wide, cracked dome of Hardstoft, beyond 
which, broadening as it pitches, it flattens out eastward in the swell which 
holds the coals at convenient depths across the Sherwood Forest area 
east of Mansfield. The Chesterfield-Clay Cross-Tibshelf syncline, two 
to four miles wide, 500-1,000 ft. deep, broadens and opens out to the 
Oxton-Thurgarton Basin of Nottinghamshire. It is bordered on the 
west by the uneven crest which brings limestone to surface at Ashover, and 
by the broken dome of Ironville, three miles long and two miles wide, in 
which the measures rise 600 ft. ‘This towards the south-east is paralleled 
by the wider anticlines of Cossal and the Erewash Valley. Further to the 
westward are the local basins of Swanwick, Ripley, and Heanor—this 
last two miles wide and 500 ft. deep—which form dimples in the terrace 
in which the margin of the coalfield extends south-westwards towards 
Derby. 
Concerning the extension of fold structures beneath the Nottingham- 
shire Trias, more, and more exact, information is desirable. In Derby- 
shire no trough or crest line ever keeps an even course, and though on a 
small-scale map we may outline in simple curves the information avail- 
able from existing pits and boring records, it is not to be expected that 
all pre-Permian folds in Nottinghamshire are broad and open. Levels in 
the Top Hard Coal between Welbeck and Ollerton rise to the eastward, 
and within two miles there is a further steeper rise to Wellow. Explora- 
tions along the line from Mansfield to Kirklington show sharp diversities 
of level of quite 1,000 ft., and to the south of this line, borings at Farns- 
field, Oxton and Thurgarton have proved 500 ft. of red Upper Coal 
Measures infolded underneath the Permian. Despite the presence of 
Upper Coal Measures in this central trough of Nottinghamshire, because 
of southward thinning of the several subdivisions of the series, it is likely 
that the deepest part of the Nottinghamshire basin is shallower by at least 
1,000 ft. than that of South Yorkshire. 
As the East Midland Coalfield fills the broad synclinorium which flanks 
the Peak uplift on the east, so the Lancashire coalfields, and whatever 
there may be beneath the plains of Cheshire, occupy the deeper downfold 
which abuts upon it from the west. Extended Charnwood, being more 
rigid, has been given greater elevation than the prolongation of the 
Longmynd, but west of this latter under the great oval area which extends 
from Manchester to Shrewsbury (sixty miles), and from Chester to Con- 
gleton (thirty miles), Carboniferous rocks are so deeply depressed and 
covered with ‘Trias as to have remained unproved. A borehole 2,500 ft. 
deep at Plumley near Northwich ended in Keuper, and under the central 
500 ft. of Lias proved at Prees the basin is probably deeper still. 
The fall-off westward from the Peak within the East Lancashire coal- 
field to Manchester, is amazingly steep, 7,000 ft. within the six miles of 
mining ground between Oldham and Manchester, 3,500 ft. in an unbroken 
two-mile dip-slope under Stockport town ; and the whole thickness of 
