1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



phism is afforded by Mofettes, where the sulphuro-hydrous emana- 

 tions turn the cretaceous Hmestone into gypsum along the lines of 

 fissure which they permeate*. M. Favre, as before stated, has shown 

 that the period when the porphyries called melaphyre were erupted 

 agrees well with this hypothesis, and that the heat and gases disen- 

 gaged diuing such volcanic outbursts might well have transformed 

 the calcareous into magnesian rocks. Thus it is supposed that the 

 carbonate of lime containing shells of the Jurassic epoch has been 

 slowly transformed into magnesian carbonate, and perhaps an increase 

 of volume was gradually acquired by the gypseous and dolomitic 

 masses in proportion as they derived fresh accessions of mineral 

 matter from below. If so it may have caused expansion, and have 

 furnished an irresistible lateral pressure. 



If in the central parts of the Alps we suppose heat to have accom- 

 panied the metamorphic action which has converted into gneiss and 

 mica-schist, not only the Jurassic and cretaceous, but even certain 

 eocene strata, this same heat must have caused many kinds of rock 

 to expand, and might, in this manner, slowly give rise to the sideway 

 thrust exhibited in the curved beds on either flank of the chain. It 

 is now known that granite and sandstone, while sohd, expand and 

 contract, even under such a range of atmospheric temperature as the 

 difference of a Canadian winter and summer produce. We must 

 also take into account that highly inclined or vertical argillaceous 

 strata, such as the flysch, would shrink when heated, and give off 

 their water ; while other rocks, ranged side by side, might be simul- 

 taneously expanding or partially melting, so as to occupy more room, 

 and that the clays might thus be pressed into sohd shales and ac- 

 quire irregular and complicated curves. The irregularity and con- 

 fusion would be greatly increased by local variations in the composi- 

 tion of the stratified deposits, whether in the direction of their strike 

 or dip, and also by the unequal intensity of the heating and cooling 

 processes, whether the central be compared with the lateral parts of 

 the chain, or the superficial with the internal parts. Yet we cannot 

 feel sure, that were such mighty changes now in progress in any 

 range of mountains subject to earthquakes, such as the Andes or 

 Himalaya, we could guess at the direction of the movement, for the 

 contraction or expansion of mineral masses might be carried on as 

 * Bulletin, 2nd Series, vol. vi. p. 124. 



