370 On Mineral Metamorphism. 



high teraperatiu'e of the injected mass, the slaty substance 

 may at the same time have i-eceived a higher crystalline 

 character, and have been developed as mica. East from 

 Stockholm lies the quarry of Yttei'by, so well known to all 

 mineralogists, where, according to Von Buch, we have good 

 illustrations of metamorphosis by injection. Possibly this 

 explanation of metamorphosis and injection may also be ap- 

 plied to the gneiss of the Outer Hebrides, where, by the rami- 

 fication of the many granitic veins, the original mass is, in 

 some instances, almost supplanted. Molten metallic sub- 

 stances also may have mixed, by injection, with the adjoin- 

 ing rock ; and Fournet is inclined to attribute to this cause 

 not only the origin of the reticulated ramified ores in many 

 mines, but also that of great masses, or of kidneys of ore, 

 isolated on every side ; the nearly mined-out nodules of py- 

 rites of copper at Chessy, near Lyons, of manganese-ore near 

 S. Marcel, in the valley of Aosta, of fahl-ore in Anniviers, 

 and of white-lead in the Maurienne have, according to his 

 view, originated thi'ough injection. 



General Metamorphic Processes. 



The difficulties which at present stand in tlie way of an 

 explanation of those metamoi'phoses which occur most fre- 

 quently, and in the greatest masses, are of diff'ei'ent kinds. 

 In several cases, tlie idea of a transformation appears contra- 

 dictoi'y to our chemical and pliysical laws, such as formerly 

 was the case with the metamorphosis of carbonate of lime 

 into marble by fusion, with the sublimation of silica, of oxide 

 of iron, and of charcoal, and with the formation of felspath, 

 and other minerals in the dry way. The explanation of still 

 existing, seemingly contradictory facts must be looked for 

 from the progress of science. In other cases, the metamor- 

 phosis extends to masses, the thickness of which far exceeds 

 the limits of the observed influence of molten substances on 

 the rocks adjacent to them, whilst mountains, many thousand 

 feet thick, have been influenced by it. Besides, it frequently 

 happens that we discover no eruptive rock to which we might 

 ascribe the metamorphic influence. In many parts of the 

 Alps, for instance, we may perceive the influence of the crys- 



