60 SECTIONAL ADDRESSES 
was progressive until 10,000 ft. of pre-Coal Measure sediment was accom- 
modated. Three thousand five hundred feet of alternating Visean shales 
and reef knolls in this mid-Pennine trough contrast sharply with the 
equivalent 400 ft. of Great Scar Limestone and overlying shale deposits 
on the adjoining Ingleborough block. 
Across North Wales and the southern Pennine district, Visean sedi- 
ments are mainly bands and banks of shallow-water limestone, 1,800 ft. 
thick at the head of the Vale of Clwyd, and a little more in the open section 
along the Wye Valley in Derbyshire. Locally in the High Peak district, 
and to a much greater extent where pierced by borings in search of oil 
beneath the Derbyshire and Staffordshire Coalfields, these limestones are 
interstratified with submarine eruptive products. ‘Towards the Midlands 
the amplitude of Visean movements was less, and as the marginal beds of 
limestone lap against St. George’s Land, though all the subdivisions are 
represented, their total thickness has diminished to about 1,000 ft. on the 
northern flanks of Charnwood, and to less than 300 ft. east of the Wrekin 
towards the Severn Valley. 
Visean deposits of the Midland Province end with shallow-water lime- 
stones containing the D3 facies fauna, which may or may not belong to 
one horizon. At some places cherty beds pass up to earthy ‘ black beds ’ 
and bituminous shales. Elsewhere the last of the grey limestones are 
impersistent shell banks and limestone breccias, and there is striking 
evidence of an interformational non-sequence. With application of 
modern zonal methods to the faunas of the shales which overlie the lime- 
stones, it has been recognised that in Pendle, between the topmost Visean 
limestone and the beds with faunas identical with the lowest Edale shales 
of Derbyshire, at least 3,000 ft. of land waste was accommodated. Lower 
Lancastrian shales and grit bands are 2,000 ft. thick in Staffordshire,? but 
have not been recognised in the Derwent Valley, so in Peakland the non- 
sequence may become an unconformity. Transgression near the same 
horizon has been followed along the edges of the Craven-Ingleborough 
block, and the relation of the Holywell shales to the underlying cherts and 
Cefn-y-fedw series in North Wales requires a similar explanation. ‘These 
evidences of structural disturbance are not regular, and whether we regard 
them as marking areas of local uplift, or attribute the non-sequence to 
cessation of downward movement, we must recognise that they coincide 
with arch folds which now dominate the local structure. 
Most important of the early Lancastrian upfolds, from the point of 
view of coalfield distribution, is the limestone plateau outcrop, the “ massif ’ 
of the High Peak of Derbyshire.2 Its margins have steep dips, but 
though its place is the north-west extension of the Charnwood Pre- 
Cambrian platform, there is underground evidence that its topmost lime- 
stones extend widely in all directions beneath the overlying shales,* and 
it cannot be accepted either as reef mass or as a pre-Lancastrian horst. 
2S. W. Hester, ‘The Millstone Grit Succession in North Staffordshire,’ 
H.M.G.S. Summary of Progress for 1931, Pt. II, p. 34 (1932). 
3 W. G. Fearnsides and others, ‘ The Geology of the Eastern part of the Peak 
District,’ Proc. Geol. Assoc., vol. 43, p. 152 (1932). 
4 T. Sington, ‘The Search for Petroleum in Derbyshire now in progress,’ 
Trans. Inst. Min. Eng., vol. 57, p- 25 (1919). TIF 
