474 Corre&'pondence. 



rock." Since that time I liave been confirmed in my opinion by 

 local geologists, so that I have now no doubt upon the matter. The 

 same reasoning which proves that the Magnesian Limestone, forming 

 the base of the Permian system, reposes directly on unproductive 

 Millstone-grit from Barnard Castle to Harrogate, shows exactly a 

 like sequence of rocks through Knaresborough, Plumpton, and 

 Bramham Park, the only difference beiag that the coarse millstone 

 at Plumpton is coloured red by peroxide of iron, certainly no 

 suificient reason in my judgment for claiming it as Permian. I 

 should not have troubled you with this letter had not I deemed 

 it right to lose no time in warning people from searching for coal in 

 the Millstone-grit of Plumpton, which is not a locality where there 

 is any fair probability of finding a profitable seam of coal, but a 

 place where no productive coal-beds can reasonably be looked for. 



I remain, yours truly, 



E. W. BiNNEY. 



Eavenscliffe, Douglas, Isle of Man, 

 Sept. l-Oth, 1866. 



EIVER-DENTJDATION OF VALLEYS. 



To the Editor of the Geological Magazine. 



Sir, — Those who are acquainted with the region of the Lower 

 Carboniferous Eocks on the borders of Lancashire and Yorkshire — 

 forming the great anticliaal ridge between the coal-fields of these 

 two counties — cannot fail to have been struck with the characteristic 

 features of its valleys. They consist for the most part of narrow 

 winding channels — bounded by steep sides, or cliffs of grit or shale 

 — intersecting flat-topped or gently slojjing moorlands of Millstone 

 grit. These valleys generally contain rapid brooks and torrents — 

 which are often swollen by heavy rains — and in their course carry 

 away large quantities of material from the bottom and sides of their 

 channels. It is, in fact, one of those districts where it might be 

 supposed the theory of the sub-aerial or river-denudation of valleys 

 could be most satisfactorily illustrated. This is certainly true in the 

 great majority of instances. When the valleys contain brooks — 

 having some relationship to the size of these valleys themselves — the 

 process of scooping the ravines is palpable to every observer ; but 

 that the theoiy is not capable of imiversal application seems to me 

 equally clear from the fact that some parts of the deepest and most 

 sharply sculptured valleys contain no streams whatever, owing to 

 their crossing watersheds. I shall briefly notice a few examples, 

 illustrated by cross-sections, of which the outlines have been drawn 

 to natural scale for the contour lines on the Ordnance Maps. They 

 are therefore true to nature, and are consequently less striking than 

 when actually seen on the spot eaid fore-shortened. But their real 

 proportions would be more evident did space admit of the lateral 

 extension of their sides. 



