18<38.] HULL— LINES OF ELEVATIOy. 327 



it here, because it shows, by reasoning backwards, that the Lancashire 

 Jlexures are also anterior to the Permian period. 



But, besides this indirect, there is also direct evidence of the age 

 of the flexures in Lancashire. At several points along the nortlicni 

 flanks of the Pendle range, we find joatches of more recent strata, 

 resting on the denuded edges of the Carboniferous rocks. Some of 

 these may be of Triassic age; but, beyond question, others are refer- 

 able to the Permian age, such as the red sandstones and magnesian 

 limestones of Skillaw Clougli and Bentley Brook, near Bispham, de- 

 scribed by myself in one of the memoirs of the Geological Survey *. 

 These Permian beds rest on others belonging to the Millstone-grit 

 series, near the south-western termination of the Pendle range of 

 hills. Now, from the known thickness of the Carboniferous series 

 in this part of Lancashire, we may calculate approximately the 

 amount of denudation before the deposition of the Permian strata ; 

 for as these latter rest on the lower beds of the Millstone -grit, and 

 as there does not appear to be any material break in the succession 

 of the Carboniferous strata, it is clear that there must have been 

 swept away part of the Millstone-grit series, and the whole of the 

 Lower, Middle, and Upper Coal-measures, amounting to nearly 

 10,000 feet of strata, which may be classified as follows : — 



feet. 



Upper, Middle, and Lower Coal-measures 8400 



Millstone-grit series (in part only) 1500 



Total quantity denuded 9900 



The above seems a large estimate, but it is not overdrawn ; and 

 it will be recollected that in my former paper, on the thickness of 

 the Carboniferous rocks in Lancashire, I have given the details of the 

 above measurements. The following ideal section (fig. 3), showing 

 the relative position of the Permian and Carboniferous beds at Par- 

 bold Hill, will render my observations more plain. 



It will be observed that at the foot of Parbold Hill the Permian 

 beds of Skillaw Clough rest on the denuded edges of the Millstone 

 series, but are again found resting unconformably on the Upper 

 Coal-measures south of the Wigan coal-field. It is clear there- 

 fore that the whole of these Coal-measures, together with part of 

 the Millstone series, amounting to several thousand feet, have been 

 swept away previously to the dej^osition of the Permian beds along 

 the northern boundary of the coal-field. This uprising of the Mill- 

 stone-grit at Parbold Hill is merely the prolongation of the Pendle 

 range, as stated above (p. 323). 



With the proof afi'orded by the Permian beds at Bispham of the 

 age of the upheaval and denudation of the Carboniferous Eocks at 

 Parbold Hill, at the extreme w^est of the Pendle range, and wdth 

 the evidence of the Permian beds of Yorkshire at the opposite end, 

 it is of little importance to my purpose what may be the ages of 



* ' Gi-eology of Wigan,' 2nd edit. (Mr, Binuey, F.R.S., fully admits these 

 beds to be of Permian age.) 



VOL, XXIV. — rAKT I. 2 a 



