250 EXPERIMENTS ON METAMORPHISM AND 



jected in tlio state of paste sometimes show but a scarcely perceptible 

 alteration, even in their immediate contact with it.* 



The eruptive rocks other than granite in like manner appear to 

 have been formed through the co-operation of water, and for the most 

 part at a temperature much lower than had been supposed, t But if 

 the eruptive rocks themselves have been dispossessed of the prestige 

 of high temperature which they liave so long enjoyed, much less could 

 their heat alone have produced the energetic effects which are often 

 attributed to them. 



Thus by three different ways the conclusion has been arrived at 

 that water, aided by certain substances, has nearly everywhere been 

 a powerful co-operator with heat in the metamorphism as well as in 

 the formation of the principal metalliferous deposits, and of the 

 eruptive rocks themselves. 



I have spoken of the first observations which disclosed the meta- 

 morphic state of certain dolomites. Since then this origin has been 

 attested in different countries. Lardy, in his excellent memoir 

 on the geognostic construction of St. Gothard, (1829,) remarks that 

 dolomite and gypsum must have had some connexion with the opening 

 of the crevasse which forms the valley of the Tessin.:}: The polypiers 

 ■changed into dolomite, and found at Gerolstein by de Verneuil, 

 have, moreover, furnished in favor of the transformation of this rock 

 an argument of which Elie de Beaumont long since showed the 

 weight. 



Elie de Beaumont, supporting his idea on the remarkably po- 

 rous and cracked state of many dolomites, such as those of Tyrol, Lu- 

 gano, and of Franconia, proved as long ago as 1829 that this structure 

 was owing to an epigenesis, and the substitution of carbonate of mag- 

 nesia for carbonate of lime in equivalent proportions.§ 



As to the manner in which this substitution may have taken place, 

 the study of the dolomites and gypsums of the valley of the Tessin 

 had suggested to de Collegno, in 1834, that the carbonate of lime 

 had probably been transformed simultaneously into gypsum and dolo- 

 mite by the action of mineral waters, the traces of which he even 

 investigated in the Val. Canaria.H It was this idea which afterwards 

 led Haidinger and de Morlot to imitate dolomiteH artificially. 



* M. Delesse has recently well summed up the facts which prove it, including: with them 

 his own observations on the metamorphism of contact. — (Bulletin de la, Societii Geologique de 

 Franze, 2d scries, vol. xv, p. 728.) 



Henry Rose has also recently put forth arguments to the same purpose: Ueber die 

 Verschiedenen zustande der kieselsaiiie Poggendorff's Annalen, 1859. 



f Tlxe aV)ove cited memoir of Mr. Delesse enumerates the principal proofs. 



"^ Denkschrift der Schweizerischen Gesellschaft , vol. i, p. 200. 1829. 



§Note sur la forme la plus ordinaire de objections relative a Torigine de la dolomie. — 

 Anilities des Sciences Naturellea, vol. xviii, p. 269, 1829. — Bulletin de la Societii Geologique de 

 France, vol. viii. p. 173, 1826. 



II Notes sur quehjues points des Aljies Suisses — (Bulletin de la Sodelii Giologique de France, 

 vol. vi, p. 110, 183-i.) 



^ Some savants, among others, Daubeny, Leube and Grandjean, consider dolomite 

 as the result of the action of the atmospheric waters on magnesiau limestone. 



Others, as Rozet and Puggaard, have attributed an eruptive origin to certain dolomites 

 which form veins and contain embedded fragments. (Framont, Grisons, Fulda, Helsingfors, 

 and Sorrente.) 



