256 J. F. NEWSOM CLASTIC DIKES 



were formed by percolating water forming cavities and letting the super- 

 incumbent sands down into the cavities.* 



Lyell, 1839. In 1839 Sir Charles Lyell described a number of sand- 

 pipes in the chalk of Norwich-, and concluded " that the excavation and 

 filling up of the pipes were gradual and contemporaneous processes."! 



Trimmer, 1840-1855. In 1840-1855 Mr Joshua Trimmer t described 

 many sand and gravel pipes occurring in Kent and Norfolk. The cav- 

 ities containing the sand and gravel pipes are regarded by Mr Trimmer 

 as having been formed as deep, narrow potholes by the wearing action 

 of the waves. Prestwich and other English writers on the subject do not 

 concur in these views of Mr Trimmer. 



Leblanc, 1842. M. Leblanc, in 1842, believed the pipes of the Paris 

 basin to be filled conduits through which underground waters formerly 

 came up, carrying with it the materials found in the pipes.§ 



Melville, 1843. In 1843 Mr Melville called attention to pipes in the 

 Tertiary of the Paris basin and gave sections to illustrate his view of 

 the manner in which waters passing down into the strata around the 

 Paris basin could have been forced up through the strata into the sea, 

 carrying up any soluble or insoluble materials they ma}^ have collected. || 



Weissenbach, 1850. In 1850 Weissenbach mentioned clastic dikes or 

 " veins " which occur near Naulitz.^ 



Prestwich, 1854. In 1854 Joseph Prestwich described a large number 

 of sand and gravel pipes in the Tertiary of the TiOndon district, and held 

 the view that these pipes had been formed by the superincumbent sands 

 and gravels being let down into cavities formed in the underlying beds 

 by percolating waters. ** 



His conclusion regarding these phenomena is stated as follows : 



*'I view these sand and gravel pipes in the chalk and other soft calcareous strata 

 as extinct natural water-conduits, which the waters, at different periods, throug:h 

 incessant filtration from a higher water-bearing stratum in their tendency to reach 

 a lower level, gradually and quietly wore for themselves by their solvent action 

 alone; the size of the pipes mainly depending both upon the length of time the 

 operation continued, and also upon the extent of difference of level between the 

 two water-surfaces." 



* Trans, of the Brit. Assoc, for 1839, p. 76. 



t London and Edinburgh Phil. Mag., 3d series, vol. xv, Oct., 1839, p. 257. 



JProc. of the Geol. Soc, 1840, vol. iii, p. 185; 1842, vol. iv, p. 6; Jour, of the Geol Soc. of London, 

 1844. vol. i, pp. .300-317; 18.52, vol. viii, p. 275; 1854, vol. x, pp. 231-240; 1855, vol. xi, pp. 02-64. 



g Bulletin de laSociete Geologique de Fra'nce, ler .s^rie, xiii, 360-366, Paris, 1842. 



II Bulletin de la Soci6t6 Geologique de France, ler s6rie, xiv, Paris, 1843. De la theorie des puits 

 naturels, pp. 182-194. 



^Gangstudien Oder Beitrage zur Kentniss der Erzgange ; Herausgegeben von Bernard Cotta ; 

 Erster Band ; Freiberg, 1850. Oeber Gangformation, von C. G. A. v. Weissenbach, pp. 16, 17. 



** Quart. Jour, of the Geol. Soc. of London, vol. ii, 1S55. On the origin of the sand and gravel 

 pipes in the chalk of the London Tertiary district, by Joseph Prestwich, pp. 64-84. 



Ibid., vol. x, pp. 222-224 and 241. 



