372 PASSAGE OF GNEISS INTO GRANITE. [Ch. XXVI. 



crystalline, but the granite, on the contrary, softer and less 

 perfectly crystallized near the junction *. 



It will appear from sections described by M. Hugi, that 

 some of the secondary beds of limestone and slate, which are 

 in a similar manner overlaid by granite, have been altered 

 into gneiss and mica-schist f. Some of these altered sedimen- 

 tary formations are supposed, by M. Elie de Beaumont, to 

 be of the age of the lias of England, and others to be even as 

 modern as the Jurassic or oolite formations. 



We can scarcely doubt, in these cases, that the heat com- 

 municated by the granitic mass reduced the contiguous strata 

 to semi-fusion, and that on cooling slowly the rock assumed 

 a crystalline texture. The experiments of Gregory Watt 

 prove, distinctly, that a rock need not be perfectly melted in 

 order that a re- arrangement of its component particles should 

 take place, and that a more crystalline texture should ensue. 

 We may easily suppose, therefore, that all traces of shells and 

 other organic remains may be destroyed, and that new chemical 

 combinations may arise, without the mass being so fused as that 

 the lines of stratification should be wholly obliterated. 



In allusion to the passage from granite to gneiss before 

 described, Dr. Macculloch remarks, that 'in numerous parts of 

 Scotland, where the leading masses of gneiss are schistose, 

 evenly stratified, and scarcely ever traversed by granite veins, 

 they become contorted and irregular as they approach the 

 granite ; assuming also the granitic character, and becoming 

 intersected by veins, numerous in proportion to the vicinity of 

 the mass. The conclusion/ he adds, 'is obvious; the fluid 

 granite has invaded the aqueous stratum as far as its influence 

 could reach, and thus far has filled it with veins, disturbed its 

 regularity and generated in it a new mineral character, often 

 absolutely confounded with its own. And if the more remote 

 beds, and those alternating with other rocks, are not thus 



* Elie de Beaumont, Sur les Montagues de 1'Oisans, &c. ; Mem. de la Soc. 

 d'Hist. Nat. de Paris, tome v. 



t Natur, Historische Alpenreise, Soleure, 1830. 



