352 TYXEDALE ESCARPMENTS; 



by land-snails, and believed to have been produced by a process 

 of boring, in effect like that of the marine stone-boring molluscs. 

 Dr. S. P. "Woodward, also a great authority, considered these 

 honcy-combings to be purely atmospheric, — like the aerial pot- 

 holes just described. In opposition to Dr. Buckland's observa- 

 tion that they occur mainly on the lower or sheltered surfaces 

 of ledges, he remarked them ** always on the windward side." 

 The snails, according to "Woodward, were only in temporarj' 

 possession.* 



"Without pretending to enter authoritatively into the niceties 

 of this question, I may be allowed to give the results of obser- 

 vations among Northumbrian limestones. The surface of wea- 

 thered joints is apt to have a smoothly dimpled and dotted 

 appearance, rather like dough marked with the tips of the fin- 

 gers, and then somewhat drawn out in one direction, — that of 

 stratification in the stone. This is unquestionably due to wea- 

 thering — chiefly to solvent action. The deepening of the dimples 

 into sacs might seem to be simply a continuation of the same 

 process. This in many cases, however, it does not seem to be. 

 If largely produced by solvent weathering, the deepening would 

 proceed so as to allow water to fill the cups, or at least to keep 

 them moister than the adjacent stone. In two excellent groups 

 of perforations I have examined, one on the north bank of tlic 

 stream bounding the lower end of the enclosure in which the 

 Swinburne stone stands, the other in Gunncrton Nick, it is an 

 almost invariable rule that tlie cavities ascend fi'om tlieir entrance 

 in a way fitted to keep the interior dry. In the Swinburne group 

 several of the holes — smooth and bulbous as usual, arc entered 

 as the bowl of a pipe is entered from its stalk, their entrance 

 being no more than half their interior width, and the bowl ascend- 

 ing vertically for some three inches. In both places they abound 

 much more on faces of limestone to leeward of the prevalent wes- 

 terly winds ; and I may remark, that among the exposed uplands, 

 where tlie aerial pot-holes are most abundant, I have souglit in 

 vain for "boringn." 



• II. W W l.s 111 on (looiopy of WclN. Proc. of Somerset Arch. nii<i N.ii. Ili-it S.ii-. 



lt)7d. 8cc .•<-" i.i^ (jCoI. uf Engluiid mui Waloi. 



