HIND : CARBONIFEROUS ROCKS OF THE PENNINE SYSTEM. 449 
The Yoredale series have the following general sequence : — 
Sandstone, 
Shale, 
Limestone, 
and da capo, which denotes an area of clear sea unaffected by sedi- 
ment, invaded by detrital mud at first, and later by lieavier detrital 
sand. Then a condition when detrital matter was no longer carried 
so far south, and a return of a clear sea with conditions suitable for 
the environment of animals producing calcareous matter. This 
change may have been brought about either by the formation of a 
bar which prevented the carriage of sediment to the south, or an 
oscillation of level sufficient to permit the repeated advance and 
retreat of conditions from north to south and vice versa. 
South of Derbyshire we know that the Lower Carboniferous 
rocks soon disappear. In South Staffordshire the Coal Measures 
rest immediately on the upturned edges of the older Palaeozoic rocks. 
In the Coalbrookdale coalfield the whole of the Carboniferous rocks 
below the Coal Measures are represented by about 40 to 80 feet of 
limestone and 10 feet of calcareous sandstones and shales, and sand- 
stones. At Steeraways, five miles further west, on the S.E. flank 
of the Wrekin, the whole deposit is only 50 feet, showing the rapid 
thinning out of these beds. 
There is little or no doubt that a ridge of land extended from 
east to west across England and Wales, and probably as far as the 
Wicklow Mountains, throughout Carboniferous times, too narrow 
and steep to supply any amount of detrital sediment, and probably 
the deepest part of the Carboniferous Limestone sea in the British area 
was a little north of this ridge. This pre-Carboniferous ridge, therefore, 
forms the south boundary of the great Pennine Carboniferous basin. 
Of Carboniferous deposits eastward we know Httle or nothing, 
but south-east in Belgium the limestone is of very considerable 
thickness and is undi voided by shales and sandstones, and the fauna 
is practically that found in the limestones of Derbyshire, Clitheroe, 
Cracoe, and Settle. At Clavier and Vise the limestone is succeeded 
by a series of shales, black limestones, sheets, and gannisters 
containing the typical Pendleside fauna. On the western side of 
M 
