EARTH-MOVEMENTS DURING CARBONIFEROUS TIMES. 377 
existing between the Charnian axis and these pre-Carboniferous 
rocks exposed near Ingleborough has been mentioned, so that 
we may assume the possibiUty of an extension of the Charnian 
axis under the Pennines. The fracture of the Silurian floor 
that caused the Craven faults would destroy the stability of the 
ridge if it existed, and therefore the absence of any perceptible 
barrier between the Lancashire and Yorkshire coalfields up to 
the horizon of the Silkstone coal of Yorkshire (equivalent of the 
Arley Mine of Lancashire) is not surprising. The correlation 
of the seams up to this horizon in the North Staffordshire, Lan- 
cashire, and Yorkshire coalfields is convincing evidence that 
the Pennine barrier did not exist in Lower Coal Measure time. 
There is little or no evidence of thinning in the Middle Coal 
Measures on the Yorkshire side of the Pennines, but on the 
Lancashire side there is marked thinning of the L'pper Coal 
Measures against the Pennines. There is additional evidence 
in the difference between the Permian rocks east and west of 
the great barrier, while the absence of Upper Coal Measures, of 
a type comparable to those of North Staffordshire and Lanca- 
shire, in the Yorkshire coalfield points distinctly to a barrier 
between the two great areas of subsidence, and dates the 
appearance of the Pennine Range at the close of the Middle Coal 
Measure period. At the same time it is very probable that 
it exercised some influence between the Silkstone or Arley 
Mine period and that of the close of the Middle Coal Measures. 
Great difficulty has been experienced in correlating the seams 
that lie above the Silkstone or Arley Mine bed in the 
Yorkshire and Lancashire basins. This might be taken to 
indicate that the buried pre-Carboniferous ridge was beginning 
to come into action and acted intermittently during Middle 
Coal Measure time, at the close of which it became 
a rigid barrier separating two (subsiding areas. It has 
already been pointed out that there is an absence of evidence 
of tangential stresses having been appHed in the Yorkshire 
basin during or since Coal Measure time. On the Lanca- 
shire side there is positive evidence of a thinning of the LTpper 
Coal Measures towards their eastern margin, while the coal seams 
themselves are steeply inclined. The inference is that the 
