KIRKBY — SANDPIPES IN MAGNESIAN LIMESTONE OF DURHAM. 333 



of the pipes in the magnesian limestone offer another difficulty to 

 this theory ; I allude to those occurring in rubble, it scarcely being 

 possible that any mechanical agent, and especially the action of surf, 

 could form tubular or conical pipes, nearly two feet deep and only five 

 or six inches in width, in so loose a substance as rubble. For on 

 such a supposition of their origin, they must of necessity have 

 remained open until completed, so that their walls of loose materials 

 would be unsupported internally, besides being exposed to all the 

 disturbing influences of a littoral region — that is, according to the 

 views of Mr. Trimmer. And it is not to be supposed that these 

 pipes might have been formed prior to the breaking up of the lime- 

 stone from which the rubble was derived, for any movements suffi- 

 ciently violent to rend and break up solid beds of limestone, would 

 certainly have destroyed the pipes passing through them. 

 On the other hand, the chemical theory explains the origin of sand- 

 pipes more satisfactorily ; and though it is not altogether unobjec- 

 tionable, yet it suffices to account for their phenomena in a manner 

 that not only seems possible but very probable. Indeed, there is 

 apparently no other agency but a chemical one that could form pipes 

 under the circumstances that seem to have existed while those in the 

 chalk were being formed. It has been shown by Sir Charles Lyell, 

 and also by Mr. Prestwich, that the pipes have been eroded after the 

 alluvium covering the chalk was deposited (this is also evident in the 

 pipes of the magnesian limestone), and that the different strata com- 

 posing the alluvium have been gradually let down into the cavities of 

 the pipes in the same consecutive order in which they occur where 

 lying undisturbed on the surface of the chalk. In my opinion this 

 seems to oblige the adoption of a chemical origin of some kind for 

 the pipes ; for in what other way could they have been formed with 

 the alluvium superimposed upon the surface acted upon ? They have 

 also shown that the agent employed did not act upon the flints em- 

 bedded in the chalk ; that the surface of such flints as had been 

 extracted from the matrix in the excavation of the pipes, are not 

 worn in the least ; and that when a flint protrudes from the wall of a 

 pipe, neither is it worn or otherwise afiected, except in one instance, 

 where the protruding portion was broken off", apparently by pressure, 

 it being found embedded in the core a little lower down. Thus it 

 seems that the agent employed had power only to act upon calcareous 

 substances, and that it was powerless upon such as were siliceous ; 

 consequently that it was a chemical agent ; for it is not to be sup- 

 posed had it been mechanical that it would not have left some 

 traces of its action on the flints in the sides and cores of the pipes. 

 But if the reader will refer to the papers of these geologists, he will 

 find full particulars of these facts, and of others of equal interest and 

 importance.* 



The softened or decomposed state of the limestone forming the 



* Lyell on Sand-pipes, Lon. and Edin. Pliil. Mag. 3 ser., vol. xv., p. 257. 

 Prest-vvich on the Origin of Sand-pipes, Quart. Jour. Geo. Soc, vol. xi., p. 64, 



