Rev. J. Clifton Ward — Geology of the Lake District. 119 



without much affecting the result, that at the close of the Carbon- 

 iferous Period, the Cumbrian nucleus was elevated to its greatest 

 height as a table-land with slight ridges and furrows, the early 

 promise of mountain and valley. Uniting the summits of the chief 

 mountains by means of a plane, we restore some such plateau ; but as 

 it is certain that the denuding agents would lower the country 

 generally as well as along certain lines of valley, we must place the 

 original plateau at a higher level than any plane now joining the 

 mountain tops. Now the highest mountain, Scafell Pikes, is a little 

 above 3,200 feet in height, and there are several others over 3,000 

 feet. Might we not suppose that the original plateau stood at 

 300 to 500 feet higher than the present highest point? If so, 

 and we can form an idea of the present mean level, we get the 

 thickness of rock removed over the area of the district in the work 

 of scenic elaboration. If we take the Keswick one-inch sheet, we 

 find that of a list of 47 mountain summits in this sheet, there are 34 

 above 2000 feet in height, and 18 above 2,500 feet. Probably the 

 mean level is not less than 1,500 feet, and not much greater than 

 1,800 feet. Hence, if we assume the height of the original plateau 

 to have been 3,500 feet (which may very likely be under the 

 mark), and the present mean level to be 1,500 feet, we have to 

 account for the removal over the area in question of some 2,000 feet 

 of rock by purely subaerial agents. It should be borne in mind 

 that none of the rocks thus removed are calcareous to any degree, 

 and therefore they are not readily soluble in water; still the 

 wonder remains that, if the original plateau did not much exceed 

 300 feet above the present highest point, more has not been effected 

 by denudation during that long period from the close of the Carbon- 

 iferous to the present, for the actual amount denuded seems insig- 

 nificant indeed in comparison with that removed from the same 

 district during the Old Ked Period. Still, the changed conditions 

 may make all the difference ; in the latter case — that of the Old 

 Red — conditions the most favourable for denudation may have pre- 

 vailed — land rising scarcely faster than the rate at which the sea 

 could plane it down ; while in the case of Post-Carboniferous ages, the 

 conditions are those of a small tract of only moderately high ground 

 containing no soluble rock material, and eaten down and into by sub- 

 aerial agencies. If the basin of the Mississippi be lowered by such 

 agencies one foot in every 6,000 years, are we likely to err much if 

 we assume that this small mountain area was denuded at the rate of 

 one foot in every 10,000 years ? Calculating on this supposition, 

 the 2,000 feet removed, in the formation of mountain and valley out of 

 the rough-hewn block provided at the close of the Carboniferous epoch, 

 would represent a period of some 20 million years. In our former 

 calculation of the length of time represented by the formation of 

 of 40,000 feet of Post-Carboniferous strata, we arrived at a period 

 of 24 millions of years. 



Summary. — The foregoing time-estimates may now be placed 

 together in one column, and in parallel columns the rates of deposi- 

 tion or denudation which have been assumed. 



