REPORT ON MINERAL AND THERMAL WATERS. 37 



occurrence in such situations. The particular circumstances 

 determining the production of the one rather than the other 

 form of calcareous spar, appear to be still unexplained, for 

 stalactitical arragonite does not appear to contain any other 

 essential ingredient than carbonate of lime, and is now supposed 

 to arise from a difference of form in the integrant molecule of 

 that base*. 



Another point requiring elucidation, relates to the absence of 

 carbonate of magnesia from stalactites arising from dolomitic 

 rocks. 



Is it, that the acidulated water first dissolves the carbonate 

 of lime, before it attacks the atomic compound of lime and 

 magnesia, or that the attraction of carbonic acid for the former 

 exceeds that which it exerts for the latter earth ? 



With respect to the extrication of carbonic acid from the its quan- 

 earth, I have myself pointed outf the enormous quantity *"y- 

 evolved in the vicinity of Naples, as at Torre del Annunziata, in 

 which and in other places it frequently destroys vegetation, and 

 likewise near the axis of the Apennine chain, midway betwixt 

 the active volcano of Vesuvius, and the extinct one of Mount 

 Vultur, at the Lago d' AnsantoJ. 



Bischof§ has described its extrication, from the various mine- 

 ral waters connected with the volcanic mountains of the Rhenish 

 provinces, and likewise from dry fiissures in the ground, where 

 its escape is recognised by the stunted vegetation, and by finding 

 a number of small animals suffocated round the spot. 



LecoqII and others have mentioned the remarkable erosion 

 produced in the rocks contiguous to the mines of Pont Gibaud 

 in Auvergne, owing to the presence of this gas in the water 

 which oozes through the rocks encircling them. 



Brandes and Kruger, in their account of the mineral waters 

 of Pyrmont^, have shown, that the extrication of carbonic acid 

 is by no means limited to the spot from whence the chalybeate 



* Mr. Crosse, amongst the experiments which he detailed at the Bristol 

 Meeting of the British Association, stated, his having found that calcareous 

 spar was formed on limestone, and arragonite on slate, by the drippings 

 from the same cavern, and that he was even able by the slow action of elec- 

 tricity, to produce each of these minerals from the same water, charged with 

 carbonate of lime, according as he placed it on a piece of limestone, or of 

 slate. 



t Edinburgh New Philosophical Journal, 1835. 



X Memoir on the LaJce Amsanctus, and on Mount Vultur in Jpulia, printed 

 by the Ashmolean Society of Oxford, 1836. 



§ VulJcanische Mineralquellen, p. 251. 



II Annales Scientifiques de I' Auvergne, and Ferussac's Bulleiin, vol. xvi. 



i P. 155, et seq. See also Brandes' work on the Mineral Waters of 

 Meinburg. Lemgo, 1832. 



