C.—GEOLOGY 61 
Moreover, its monoclinal edges are plicated by pitching cross-folds, on 
whose arches are the reef knolls and beds of limestone breccia, and in 
whose troughs there is the appearance of conformity from cherty limestone 
to Lancastrian shales older than those which are continuous over inter- 
vening arches. These cross-folds have persisted as belts of instability 
throughout and beyond the period of the Carboniferous. ‘Their extended 
axial lines are marked by rapid pinching out of sandstones of the Millstone 
Grit deposits, and they line up with the steep-sided anticlines and synclines 
of the Derbyshire and Midland Coalfields. The most northerly of these 
curving cross-folds terminates and contains the High Peak limestone area, 
and beyond it there is no evidence of pre-Lancastrian uplift of any central 
Pennine fold. 
During the later Lancastrian or Millstone Grit period, and on throughout 
the Coal Measures, negative movement, though progressive, was punctu- 
ated by frequent delays. Sediment was delivered to Yorkshire in such 
quantity that it could not be accommodated until regional settlement had 
made its place. During the waiting periods therefore it drifted on 
towards Cheshire and built its lenses on the front of the growing delta. 
As sinking proceeded there was agitation in the shallows, and coarse 
material was entrapped in deepening troughs. Coarseness of sediment 
in such measures, though it must always be an index of the velocity of the 
inwash current, can in no wise be accepted as a criterion of proximity 
to a shelving shore. 
Lancastrian sediments are thickest north of the Lancashire Coalfield, 
where more than 5,000 ft. of shales and grits were accommodated. ‘The 
Millstone Grit divisions lose thickness southward round about the Peak 
district, but in Staffordshire the bore-hole at Rownall Hall, started below 
the Middle Grits, had not reached limestone at a depth of 2,700 ft.° 
Against the encircling fold which ends the limestone outcrop of the High 
Peak at Castleton, lenses of sandstone, which are exceptionally strong in 
the ‘edges’ of Kinderscout, lose half their thickness. We have no proof 
that P. or lower E. beds were ever deposited over the High Peak district, 
but mineral constitution seems to show that the coarsest Middle Grits 
were persistent from the Derbyshire Edges east of the Derwent to the 
Roaches of Staffordshire. Within the East Pennine Coalfield, deep 
borings indicate a wedging out of the whole series south-eastwards, from 
1,500 ft. thick at Renishaw to less than 300 ft. at Kelham. ‘The available 
records are all from trial oil wells in anticlinal areas, and there is evidence 
of grits and shales outcropping north-west of Charnwood, and Lower 
Lancastrian Ez shales persist beyond the Hathern boring.’ South- 
westwards across Lancashire the advancing Millstone Grit delta did not 
reach North Wales, and in 400 ft. of Holywell shales all the Lancastrian 
zones are represented. 
Despite pulsatory and progressive subsidence, the whole South Pennine 
area was filled and levelled to a plain before the period of the Millstone 
Grit was ended, and the latest G. marine band spread over and drowned 
5 H. P. W. Giffard, ‘ The Recent Search for Oil in Great Britain,’ Tvans. Inst. 
Min. Eng., vol. 65, p. 221 (1923). 
6 ‘ Wells and Springs of Leicestershire,’ p. 99. H.M.G.S. Mem. (1931). 
