KIIIKBY — SANDPIl'KS IN MAGNESIAN LIMESTONE OE DUUHAM. 333 
of the pipes in the magncsian limestone offer another difficulty to 
this theory ; I allude to those occurring in inibble, it scarcely being 
possible that any mechanical agent, and especially the action of surf", 
could forni tubular or conical pipes, nearly two feet deep and only hve 
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 
distm-bing 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 Sii' 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 dovra into the cavities of 
the pipes in the same consecutive order in which they occur where 
lying undisturbed on the sm'face 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 allu-vium sujjerimposed 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 fi^om the matrix in the excavation of the pipes, are not 
worn in the least ; and that when a flint protrudes fi-om the wall of a 
pipe, neither is it worn or otherwise affected, except in one instance, 
where the protruding portion was broken off, apparently by pressure, 
it being found embedded in the core a Uttle 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. Phil. Mag. 3 ser., vol. xv., p. 257. 
Prestwich oil the Origin of Saud-pipes, Quart. Jour. Geo. Soc, vol. xi., p. 64. 
