56 SIXTH REPORT — 1836. 



mountains of the Taunus to those of Bohemia and Silesia, and of 

 which this class of springs are among the consequences. 



Products of Before I conclude this portion of my subject, it may be pro- 

 springs. pgj. briefly to notice, to what extent mineral waters appear to 

 have afffected the geological structure of certain parts of the earth. 

 Trivial as this influence may seem at present to be, yet it will 

 be sufiicient to refer to Mr. Lyell's well-known work, as esta- 

 blishing the position, that no inconsiderable portion of the crust 

 of the globe, in volcanic countries at least, is attributable to the 

 deposits which they have occasioned. 

 Calcareous. Without pretending to describe the vast accumulations of tra- 

 vertin formed by carbonated springs, in Tuscanj', in the Cam- 

 pagna di Roma, in Hungary, &c., I shall merely remark, that 

 the resemblance, which some varieties of this deposit bear to the 

 materials of older calcareous rocks is so great, and the passage 

 from one to the other so imperceptible, that we are naturally led 

 to suspect the latter to have been often produced in the very 

 same manner. 



Thus some varieties of travertin are undistinguishable in hand 

 specimens from marble, as that formed by the waters of Civita 

 Vecchia in the Campagna*. Others, like that near the town 

 of Nonette, on the right bank of the Allier in Auvergne, might 

 be mistaken for the Juratic limestone f ; and the shelly lime^ 

 stone, now forming at the bottom of many lakes, bears the most 

 complete resemblance to certain tertiary deposits J. 



Even the concretionary structure of the limestone of Sunder- 

 land, a rock, which, though existing in the magnesian limestone 

 formation, and in the midst of a powdery variety of dolomite, is 

 itself almcst wholly calcareous, is imitated by the spheroidal 

 masses of travertin that occur at Tivoli and at Carlsbad, and 

 may have resulted from the same gyratory motion of its com- 

 ponent parts during their deposition, to which Mr. Lyell has 

 ingeniously attributed the concentric circles of the latter deposit. 

 The absence of magnesia confirms this suspicion. 



In the ocean it is probable that mineral springs fulfill a still 

 more important office — that, namely, of supplying with calca- 

 reous matter those Mollusc* which are building up extensive 

 coral reefs ; for, as I observed many years back§, the muriate of 

 lime which the ocean contains, would long ago have been ex- 

 hausted by the operations of these animalcules, supposing them 

 to have the power of decomposing it, and of appropriating its 



* Lyell's Geology, vol. i. p. 198. 



t Lecoq and Bouillct, Fues et Coupes d'Auveujne, p. 131. 



+ Lyell, Genl. D-nus., 2nd Series, vol.ii. p. 73. 



§ Jnatiyiti al Lecture on Cfmnislri/, Oxford, 1824. 



