PRESTWICH — SAND- AND GRAVEL-PIPES. 65 



the gravel-pipes, and briefly ascribed their origin to the eroding 

 action of water percolating through the gravel or sand. 



In August 1839 Dr. Buckland* read a paper before the British 

 Association, in w^hich he described several of these pipes in 

 the neighbourhood of London, and expressed an opinion that they 

 were due to the action of water, holding carbonic acid in solution, 

 constantly percolating through the same cavity, dissolving the chalk, 

 and letting down the superincumbent sand or gravel. 



Sir Charles Lyellf, in a paper on the "Sand-pipes" in the Chalk 

 near Norwich, expressed a similar opinion, gave some very illustrative 

 examples in support of that view, and concluded that these cavities were 

 " due to rain-water impregnated with carbonic acid from the atmo- 

 sphere and vegetable soil, and descending into pits or furrows which 

 may have existed on the surface of the Chalk," and *' that the exca- 

 vation and filling-up of the pipes were gradual and contemporaneous 

 processes." Sir Charles further considered "that land consisting of 

 Chalk covered by Crag was first laid dry before the origin of the 

 sand-pipes," and " that the denudation which gave the district its 

 actual valleys " must have taken place subsequently. 



In opposition to this, if it may be so termed, chemical theory, 

 Mr. Trimmer I has come to the conclusion that both in Kent and 

 Norfolk the sand- and gravel-pipes in the Chalk are to be attributed to 

 the mechanical action of the breaking of the sea on a low shore 

 antecedent to the formation of the deposit with the materials of 

 which the pipes are filled. In corroboration of this opinion, Mr. 

 Trimmer states that the pipes are vertical terminations to horizontal 

 furrows on the surface of the chalk ; that many of the flints in the 

 pipes are water-worn ; that the apices of the pipes are 3 or 4 

 inches broad, and not pointed ; that certain blocks of Tertiary sand- 

 stones on the shores near the Reculvers are marked by like pipes and 

 furrows, though of smaller dimensions (only a few inches deep and 

 wide) ; whence, as those sandstones are siliceous, the excavations on 

 them could not have been formed by the action of acidulated water ; 

 and further, that near Canterbury the sands with which the pipes 

 are filled contain much calcareous matter, and consequently that any 

 carbonic acid in the water must have been saturated by it before it 

 could have reached the Chalk. He therefore suggested that it must 

 have been mainly by the action of the waves, charged with sand and 

 small pebbles, wearing furrows and hollows on the surface, and then, 

 by the rotatory motion communicated to the water, sand, and peb- 

 bles in these hollows by the influx and reflux of the waves, that 

 these pipes were drilled. Further, Mr. Trimmer mentions that the 

 sand- and gravel-pipes are confined to the edges of the seas preceding 

 the spread of the materials, whether eocene sands, crag, or drift- 

 gravel and sand, which ultimately filled up these excavations. 



Other theories have been subsequently expounded by M. Leblanc 



* Trans. Brit. Assoc, for 1839, Sect. p. 76. 

 t L. and E. Phil. Mag. 3rd Ser. vol. xv. p. 257, Oct. 1839. 

 t Proc. Geol. Soc. 1840, vol. iii. p. 185 ; 1842, vol. iv. p. 6. Quart. Journ. 

 Ceol. Soc. 1844, vol. i. p. 300 ; 1852, vol. viii. p. 273. 



VOL. XI. — PART I. F 



