128 Professor A. Delesse on the 



cal properties of the rock result from the action of heat, 

 electricity, magnetism, pressure, as well as of all the agents 

 that can bring into play molecular attraction and repulsion. 

 The modifications in its chemical properties arise from the 

 introduction of new substances in the rock, by injection, sub- 

 limation, secretion, cementation, and especially by infiltration. 



M. Delesse then observes : — " It appears to me that the 

 crystalline limestones should be considered metamorphic, 

 though certainly they are metamorphic to very different de- 

 grees ; still they have all been subjected, since their deposi- 

 tion, to modifications in their chemical, or at least their 

 physical properties. There are, however, some limestones 

 that form an exception, namely, those which have been de- 

 posited by chemical precipitation, and which were originally 

 crystalline. These are not to be confounded with the meta- 

 morphic crystalline limestones, nor do they contain the 

 mineral characteristics of the latter. 



The crystalline limestone of the gneiss of the Vosges, 

 which, from its mineralogical and geological characters, M. 

 Delesse considers to be a metamorphic limestone, is then 

 particularly adverted to ; its characters are succinctly de- 

 scribed ; and M. Delesse proceeds to say, that probably the 

 limestone was originally deposited, either in mass from water 

 charged with carbonate of lime, or as strata by the waters 

 of the sea. The beds in which the limestone has been inter- 

 calated belong without doubt to certain divisions of the 

 Transition group ; and, moreover, all geologists who have 

 studied the Vosges have regarded the gneiss inclosing the 

 limestone as metamorphic. 



The phenomena that have produced the metamorphism of 

 the gneiss are unknown ; but a group of strata could be 

 transformed into gneiss only by the introduction of the quan- 

 tity of alkalies necessary for the production of the felspar, 

 one of the constituents of the gneiss. Further, heat must 

 have been effective in the development of the crystalline 

 structure of the limestone of the gneiss, since the limestone 

 contains spinelle, chondodrite, garnet, amphibole, pyroxene, 

 &c. ; that is to say, minerals of an igneous origin, since they 

 are found in the limestones on the flanks of Vesuvius, or in 



