272 DISCUSSIONS IF COSMOLOGY. 



the known thickness of the Carboniferous 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 Yale of 

 Clitheroe, and at the base of the Pendle 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 

 thickness of strata have been removed in some places * 



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 mile must 

 have been denuded, but we do not know how much 

 more than that may have been removed. For 

 anything which we know to the contrary, hundreds of 

 feet of rock may have been removed before the 

 dislocation took place, and as many more hundreds 



* Lyell's "Student's Manual," chap. 23. 



