EARTH-MOVEMENTS DURING CARBONIFEROUS TIMES. 373 
the older theory does not accurately represent the compUcated 
series of earth-movements that were in progress during Carbon- 
iferous times, nor the part they played in determining the present 
limits of the British coalfields. In this paper it is proposed to 
briefly discuss the effects of these movements so far as the York- 
shire, Derbyshire, and Nottinghamshire coalfield is concerned, and 
to determine, so far as is possible, their sequence and character. 
For the sake of brevity the area imder discussion will be called 
the Yorkshire coalfield. 
II. — The pre-Carboniferous Floor under Stress. 
If we knew more about the structure of the old Silurian floor 
it is very possible that we should find the present form of the 
coal basins indicated, and that in no very vague form either. 
When its various beds were subjected to the tangential stress 
that marked the post -Silurian era, the stressed rocks found relief 
in plication and fracture, with the resulting formation of its 
characteristic ridges and hollows. When equilibrium had been 
established, it is clear that the more normal phase of earth- 
movements came into operation, and the Silurian floor became 
affected by differential subsidence. That it was reaUy a sub- 
sidence is indicated by the vast thickness of sediments laid 
down. That it was differential is evident from the variations 
in the age and character of the sediments laid down in different 
areas. It wiU suffice to mention that in South Wales* there 
is an uninterrupted sequence of deposits from the base of the 
Old Red Sandstone to the top of the Coal Measures, while in 
Yorkshire the Carboniferous basement conglomerate rests on the 
upturned edges of the truncated Silurian folds. A discussion 
of other areas would serve to disclose other differences in the 
rate of subsidence. The chief exposures of pre-Carboniferous 
rocks in Yorkshire are in the neighbourhood of Ingleborough, 
and it is suggestive that their strike displays a marked tectonic 
relationship with the Charnian axis, and this suggests that, like 
that ancient ridge, the exposures in Yorkshire might be a com- 
plex of rocks older than Silurian. The significance of this re- 
lationship will be pointed out later. The coming into operation 
* A. Strahan. Geology of South Wales CoalfielcL Part I., p. 1. 
