66 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



and M. Melleville. These geologists argue, chiefly from the lenti- 

 cular shape and chemical composition of several of the large rock- 

 masses composing the French Tertiary series, and from the con- 

 nexion of the pipes with the several rock-masses in which they end 

 upwards, that such cavities are old channels connected with subter- 

 ranean sources by which water charged with calcareous matter, with 

 sulphate of lime, with sand, or with mud, has been ejected from be- 

 neath at one time into the sea of the Paris Tertiary basin, and at others 

 into its lakes. M. Leblanc"*^ connects this process with some former 

 operation like that of existing hot-springs, whilst M. Mellevillef gives 

 a section showing that when the French Tertiary area was covered by 

 the sea, the older and deeper-seated deposits beneath it, cropping 

 out on high ground inland, might conduct waters through any per- 

 meable strata down beneath that sea, and into which the waters then 

 rose through these vertical channels (puits naturels\ charged with 

 the materials, soluble and insoluble, collected during their subterra- 

 nean course. 



Other geologists, again, have referred the sand- and gravel-pipes 

 to the former action of brooks and streams, analogous to that by 

 which swallow-holes are now excavated in chalk J and limestone 

 districts ; in such a case the filling up of the cavities would be caused 

 by subsequent changes brought about upon the surface of the land. 

 That such swallow-holes must have existed at all periods cannot be 

 doubted ; but the phsenomena which they present will hardly agree 

 with that presented by the sand- and gravel-pipes : the one evidently 

 depends solely upon the action of running surface-water, and always 

 exposes open cavities, whereas the other is always in connexion with, 

 and dependent upon, some overlying stratum deposited before and 

 not after the excavation of the pipes, — are cavities formed, as it were, 

 under cover. 



With regard to the theory of ejectment, it is attended with great 

 difficulties, and, the hypothesis which I have to suggest being based 

 upon the very reverse action of injectment, I will not stop to discuss 

 it separately, as the argument brought forward in the following pages 

 will, if true, render this other theory inapplicable in this particular 

 case §. As Mr. Trimmer's views, however, will not be subject to this 

 antagonistic argument, I must notice them in greater detail, the 

 more especially as his observations are numerous and his facts are 

 carefully recorded, though I cannot agree in the conclusion which 

 he has drawn from them. 



1st. As to the connexion of furrows on the surface of the Chalk 

 with the pipes. This is an argument which suits the hypothesis of 

 the chemical theory as well as his own ; for a constant slow current 

 passing from the superincumbent strata into the pipe must, as it is 

 presumed to wear the pipe, wear furrows in the chalk before reaching 



* Bull. Soc. Geol. de France, vol. xiii. p. 360, 1842. 



t Ibid. vol. xiv. p. 184, 1843. See also Forchhammer on the tubular pipes in 

 the Faxoe Chalk, Quart. Journ. Geol. Soc. vol. vi. part 2. Miscel. p. 52. 

 i Quart. Journ. Geol. Soc. vol. x. p. 222. 

 § Not but that there may be cases in which such an agency may be applicable. 



