TRIMMER — SAND-PIPES. 63 



Mr. Prestwich exhibited sections of furrows in clay, which he 

 ascribes to the mechanical action of water. But similar furrows in 

 chalk are so intimately associated with pipes, that they must have 

 had a common origin ; and, if the mechanical action of water be ca- 

 pable of producing both pipes and furrows, why should we suppose 

 two different causes to have been acting in close contiguity for the 

 production of effects to which one of them is adequate? 



4. It has been objected that the vorticose action of water would 

 not drill a hole so deep in proportion to its diameter, as the pipes 

 in the chalk. In order to test the validity of this objection, I filled 

 a precipitating jar, 14 inches deep by 2\ in diameter, with water, 

 putting a little sand at the bottom. These proportions are, in this 

 case, nearly the same as those of a pipe 4 feet in diameter, and 24 

 feet deep. On stirring the water to the depth of less than half an 

 inch, the whirlpool thus formed speedily extended to the bottom of 

 the jar, and set the sand in motion. This action of water would of 

 itself be capable of removing so soft a substance as chalk, even with- 

 out the aid of sand and pebbles, leaving the flints undetached and 

 unabraded. The objection is thus obviated which has been raised 

 against my views, from the general condition and position of the flints 

 in the pipes of the chalk which are unabraded and on the sides of 

 the cavity, instead of water- worn and at the bottom of it. 



5. It has also been objected, that if water in vorticose motion were 

 capable of boring the pipe, it could not remove the excavated matter. 

 When I saw similar cavities forming on a chalky shore by the flux 

 and reflux of the waves, the chalk removed in the process of ex- 

 cavation was flowing out of the cavity in a milky stream. Whoever 

 will take the trouble of repeating the experiment which I have de- 

 scribed above, will find that the vorticose motion, produced in the 

 water of the precipitating jar, raises the finely comminuted particles 

 of sand from the bottom to the upper part of the vessel ; and if the 

 bottom of the whirlpool acted upon chalk instead of on glass, and if 

 the mouth of the pipe were immersed beneath a stream of water, 

 not only would a deep and narrow hole be bored in the chalk, but 

 the hole would be cleared of the waste as the drilling of it pro- 

 ceeded. 



My papers on the subject of pipes in chalk have been directed against 

 the doctrine promulgated by Sir Charles Lyell, that these cavities 

 are now in the course of formation by the chemical action of rain- 

 water charged with carbonic acid and percolating the strata above 

 them, which are supposed to have subsided, and to be subsiding into 

 the cavities. I have endeavoured to prove that their formation was 

 completed before the matter filling and covering them was deposited. 



The views of Mr. Prestwich so far coincide with those of Sir 

 Charles Lyell, that he attributes the formation of the pipes to the 

 solution of the chalk by acidulated water, after the deposition of the 

 strata above them. He considers, however, that they were formed 

 under different conditions of level from the present ; and that the 

 operation is not now in progress, except in the case of swallow-holes. 



