C.—GEOLOGY 65 
any emergence of the Don Valley fold before the Red Beds were deposited 
over it, but both in Yorkshire and in Derbyshire, where the folds are 
steeper and narrower, it is probable that by the time the latest coal streaks 
of the A. Phillipsii zone had accumulated, the workable coals lay many 
hundreds of feet deeper in the synclines than over the anticlines between. 
The latest grey beds of the Phillipsii zone pass up by alternations into 
the Red and Mottled series which for convenience is taken as the lowest 
division of the Upper Coal Measures. ‘These variegated and ill-stratified 
Brick and Tile Marls (Etruria Marls) are over 1,250 ft. thick in the 
trough of the Potteries Coalfield, and as the Ruabon Marl group in 
Denbighshire their thickness is hardly less. Of the equivalent Ardwick 
group of the Manchester syncline, over 1,000 ft. remains below the 
Collyhurst Sandstone. At Farnsfield in Nottinghamshire, some 600 ft. 
of variegated beds are preserved beneath the Permian in the deepest part 
of the East Pennine basin. In South Staffordshire, the thickness of the 
Marl group is very variable, from 800 to 150 ft. within two miles, and 
there is evidence that with redisturbance of local folds across the Black 
Country, trough-like areas were developed in which deposition kept pace 
with the sinking of the floor. In Warwickshire and in Shropshire, and 
in the south of South Staffordshire, the Marl group overlaps the Productive 
Coal Measures against the shores of islands, whose waste provided the 
fragments which compose the Espley Rocks. 
The Newcastle-under-Lyme group of the Potteries is 600 ft. thick. 
Its variegated grey and green beds mark a temporary late return to normal 
Coal Measure conditions in the south-west Midland area. As the 
Halesowen Sandstone group of South Staffordshire and Warwickshire, 
and the Coalport group of Shropshire, its component members thin as 
they overstep towards the south, and it rests with slight unconformity on 
the Old Hill Marls or older rocks below. 
Over the eastern part of the Midland Coalfield Province, the strati- 
graphical record of the early development of structures ends with the 
deposits of the A. Phillipsii zone. In the south-west, red and purple 
marls, sandstones and conglomerates, deposited in reasonably strict 
conformity upon the latest coal-bearing series, carry on the history of 
settlement and contemporaneous filling of a land-locked basin to a later 
stage. 
In North Staffordshire some 700 ft. of red, purple and grey marls and 
sandstones form the Keele group. Over the Warwickshire Coalfield and 
all round the South Staffordshire Coalfield this group maintains its 
thickness, but in Shropshire it tapers out south-westwards as it overlaps 
beyond the coalfields against the edges of older land. Upwards it passes 
into the calcareous Enville group of Staffordshire or the Corley group of 
Warwickshire, with interstratified lenses of conglomerate, and in the 
higher parts has great wedges of breccia, scree or torrent-borne products 
derived from neighbouring Lower Carboniferous, Silurian, Cambrian 
or Pre-Cambrian outcrops upraised towards the south. In southern 
Warwickshire,!° the thickness of the extended Corley group is not less 
_ 10 F, W. Shotton, ‘On the Geology of the Country around Kenilworth,’ 
Q.J.G.S., vol. 85, p. 170 (1929). 
D 
