254 M. A. Gnyoi. on the Distribit'ion of Rocks 



slightly tinged with violet, \i\ large parallelopipedal crystals, 

 often mdcles, or twin crystals, with quartz faintly violaceous ; 

 amphibole and a chloriteous substance usually replace the mica, 

 which is rare, and form here and there masses of a dark-green, 

 the size of which varies from an inch to a foot and upwards. 

 We should then be disposed to say that a fragment of a foreign 

 rock was imbedded in the mass of granite. Lastly, a talcose 

 substance of a light-green, with an earthy appearance, com- 

 municates its colour to a part of the mass. These are the 

 protogines of the chain of Mont Blanc, of which there are 

 many varieties, owing to differences in the development of 

 the crystals, in the structure, and in the abundance of the 

 talcose parts. Although these varieties seem to be found in 

 many parts of the chain, it may be said, in general, that the 

 protogines which are distinguished by the disproportionate 

 size of their crystals of felspar and gneissitic structure, be- 

 long to the needles of Chamounix, on the north-west decli- 

 vity of the chain ; those of Yal Ferret, on the north-east de- 

 clivity, have a more equal grain, although the crystals are 

 still very much developed. The protogines with small grains, 

 poor in talcose portions, or passing into true gneiss, are 

 found chiefly in the extreme north, between St Maurice and 

 Martigny, as in Mont Catogne. 



The second kind of granite differs from the preceding in 

 many chai'acters. The crystals do not exceed a medium size ; 

 Ihey are also more confusedly crystallised, and are never 

 macles, or twin crystals. The mica, or the substances which oc- 

 cupy its place, is more disseminated and of a lighter green. 

 These granites rarely contain dark masses imbedded in their 

 substance : when they do, they are inconsiderable, and less 

 distinctly defined on their edges. The talcose portions are 

 often by no means abundant, and the aspect of the rock gene- 

 rally whiter. Th( se granites come from the glacier of the 

 Rhone and the mass of the Bernese Oberland, descending by 

 the glaciers Yiesch and Aletsch, and following the right bank 

 of the Valais, whence their analogy ^ith those which issue 

 from the same masses by the valley of the Aar. 



8. The Pudding-stones of Valorsine, Avhich the beautiful 

 observations of S.xussure have rendered celebrated, are one 



