480 Correspondence — Mr. R. Craig — Mr. W. H. Penning. 



the same features as when the ice-grinding stopped. In other 

 quarries, where the covering is loose, the limestone is eroded into 

 pits, swallow-holes, and crevices, many feet in thickness being often 

 dissolved away altogether. For a long time I have been on the 

 outlook to find a section that would give the number of feet 

 destroyed by sub-aerial erosion since glacial action ceased, but failed 

 until latel3^ It was always easy enough to know how many feet had 

 been removed as a whole, but there was no data to show where glacial 

 action had stopped, and sub-aerial erosion had commenced. How- 

 ever, a section has been laid open that gives a close approximation. 



In the upper half of this limestone various bands of nodular flint 

 occur, three of which bands are prominent ; and are divided from each 

 other by five feet of intervening limestone, and lesser flint bands. 

 In one section, where about 20 feet of limestone had been removed 

 by erosion, the three flint bands were found nearly entire, while the 

 limestone was gone. It was therefore clear that all of it, from, 

 at least, the upper flint band, had been destroyed by such sub-aerial 

 erosion since glacial action stopped — the minimum quantity eroded 

 cannot be less than twelve feet, probably as much as fifteen feet. 



Having measured the rate of erosion for thirty years, by taking 

 the limestone surface with a plastic substance, and replacing the loss 

 through erosion with water, and thus calculating the loss, I find 

 from this, that it is being denuded at the rate of iV of an inch in 

 fifty years, or one foot in 9600 years. If this be anything 

 approaching an average, it would take 115,000 years to denude 

 twelve feet, or 144,000 to reduce fifteen feet, the probable quantity 

 destroyed. 



This gives an approximation of the time that has passed away 

 since glacial action stopped, and sub-aerial erosion commenced. 

 Still a considerable period may have been taken up in denuding 

 clay left by the ice ; but on this I do not enter, farther than to say 

 that the section being on a very small plateau, on a water-shed, and 

 I believe that very little Boulder-clay would be left upon it, and 

 that sub-aerial erosion would commence shortly after glaciation had 

 stopped. Egbert Craig. 



Langside, Beith, Sept. ith, 1878. 



THE DIVINING ROD. 



SiK, — The following extract from the Marlborough Times of 

 Aug. 24th should possess great interest for readers of the Geol. Mag. 



London, 6th Sept., 1878. W. H. PENNING. 



Search for Water. — A person from Colerne, near Bath, who professes to haye 

 the gift of divining ■where a spring of water is to be found by means of a small 

 piece of white thorn of this year's growth in the shape of a V, was at "Wootton 

 Bassett the other day and operated on Mr. Hart's premises, pointing out a site for 

 another well for his brewery — even the depth at which water would be likely to be 

 found being designated by him. It is said that those who possess this quality are 

 extremely few. Two or three years since a person named Weare resided in the 

 town who used the divining rod, and who had a most implicit and sincere belief in 

 his powers, for which he could not account, and really to a looker on the rod 

 appeared to move quite independently of him and in fact to be beyond his control. 

 The operator on this recent occasion stated, we believe, that he had been successful 

 in discovering springs by this means on more than two hundred occasions without a 

 single failure. (!) 



