172 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 13, 



of gypsum. In like manner, as the dolomite is the metamorphosed 

 limestone, the lines of bedding and fossils of which are frequently left 

 in the transformed masses, so are the great accumulations of gypsum 

 apparently deposits of carbonate of lime which have been changed 

 into the sulphate of lime. Whether on the highest part of the route 

 over Mont Ceuis, or in the deep gorges of the Tarentaise or the Mau- 

 rienne, or in the Allee Blanche, the valley of Cormayeur and other 

 tracts around Mont Blanc, the same lesson is invariably to be read off ; 

 viz. that great bands of limestone have been here and there, and often 

 along zones of some length, converted into gypsum. For, the strati- 

 fication and even the colours of the original mass so remain, the thick 

 and thinly laminated beds of various tints of white and brown and 

 grey limestone are so preserved, that I have frequently walked up to 

 a rock under the persuasion it was a continuation of the limestone of 

 an adjacent escarpment, until my hammer undeceived me. Whilst 

 expressing my own belief, I must say that it is chiefly a development 

 of the view entertained by the deceased INIr. Bakewell, who as early 

 as 1820, when residing at the baths of Brida in the Tarentaise, came 

 distinctly to the conclusion, that the great limestones of Savoy be- 

 longed to the upper secondary strata, and that the gypsum, whether 

 anhydrous or granular, was subordinate to and interstratified with 

 them. That author had also the merit of remarking how these sub- 

 crystalline rocks of secondary age were associated with talc schists 

 and mica schists, and were all connected with the alterations due to 

 the action of heat and the formation of granitic rocks * . 



I will not here enter at greater length into the question of whether 

 these masses of stratified gypsum, which sometimes occupy entire 

 mountains, were contemporaneously deposited with carbonates of lime. 

 If the presence of such thick accumulations of anhydrous gypsum be 

 not due to metamorphism, I would ask those who entertain the op- 

 posite view to explain, how they can suppose that in the very same sea 

 and at the very same period, carbonates of lime should have been 

 deposited along many leagues of the sea-bottom, and that all at once 

 the same laminae of deposit should have been formed of sulphate of 

 lime ? How dovetail the one into the other ? On the other hand, 

 nothing is so natural as that the evolution of heat and gas in a region 

 permeated by igneous rocks should have converted the original car- 

 bonates into sulphates in one tract, and have left the limestones un- 

 changed in another. 



Fortunately, indeed, nature still exhibits in the Alps of Savoy 

 the process by which this conversion may have been effected. 

 The well-known thermal waters of Aix, which rise from a great line 

 of fissure, and contain a notable quantity of sulphur, do now actually 

 change the ordinary Jurassic limestone into the sulphate of lime, 

 wherever their hot vapours charged with sulphuric acid have access 



* See Bakewell's Travels in the Tarentaise, &c., vol. i. pp. 276 et seq. and pp. 

 289 to 311. Showing, according to M. Charpentier, that the granular gypsum of the 

 Alps is simply the decomposed anhydrite, Mr. Bake%vell points out the existence 

 of a carbonaceous stratum in the heart of a thick band of gypsum. 



