312 Probable Origin and Age of the Sun. [July? 
Carboniferous strata have been removed by denudation from 
the present surface. 
Between Bendrick Rock and Garth Hill, South Glamor- 
ganshire, a mass of Carboniferous and Old Red Sandstone, of 
upwards of 9000 feet, has been removed. At the Vale of 
Towy, Caermarthenshire, about 6000 feet of Silurian and 
5000 feet of Old Red Sandstone — in all about 11,000 vertical 
feet — have been swept away. Between Llandovery and 
Aberaeron a mass of about 12,000 vertical feet of the 
Silurian series has been removed by denudation. Between 
Ebwy and the Forest of Dean, a distance of upwards of 
20 miles, a thickness of rock varying from 5000 to 10,000 
feet has been abstracted. 
Prof. Hull found* on the northern flanks of the Pendle 
Range, Lancashire, the Permian beds resting on the denuded 
edges of the Millstone Grit, and these were again observed 
resting on the Upper Coal-measures south of the Wigan 
coal-field. Now, from the known thickness of the Carbon- 
iferous series in this part of Lancashire, he was enabled to 
calculate approximately the quantity of Carboniferous strata 
which must have been carried away between the period of 
the Millstone Grit and the deposition of the Permian beds, 
and found that it actually amounted to no less than 
9,900 feet. He also found in the Vale of Clitheroe, and at 
the base of the Pendie Range, that the Coal-measures, the 
whole of the Millstone grit, the Yoredale series, and part of 
the Carboniferous Limestone, amounting in all to nearly 
20,000 feet, had been swept away — an amount of denudation 
which, as Prof. Hull remarks, cannot fail to impress us with 
some idea of the prodigious lapse of time necessary for its 
accomplishment. 
In the Nova Scotia coal-fields one or two miles in thick- 
ness of strata have been removed in some places. t 
It may be observed that, enormous as is the amount of 
denudation indicated by the foregoing figures, these figures 
do not represent in most cases the aCtual thickness of 
rock removed from the surface. We are necessitated to 
conclude that a mass of rock equal to the thickness stated 
must have been removed, but we are in most cases left 
in uncertainty as to the total thickness which has actually 
been carried away. In the case of a fault, for example, 
with a displacement of (say) one mile, where no indication 
of it is seen at the surface of the ground, we know that 
on one side of the fault a thickness of rock equal to one 
* Quart. Journ. Geol. Soc., vol. xxiv., p. 323. 
f Lyell’s Student’s Manual, chap. 23. 
