On Mineral Metamorp/tisjii. 371 



talllne slate rock on the adjacent limestone. The latter, for 

 several fathoms upwards, is bright or variegated crystalline, 

 or changed into siliceous limestone or dolomite (Urbachvale, 

 Grindelwald, Morcles, Oisans); but if the crystalline slates are 

 themselves also of metamorphic oi'igin, then we look in vain 

 for a focus from which their metamorphoses can have pro- 

 ceeded. The greatest difficulty, however, lies in the fact, 

 that metamorphic rocks are frequently separated by a series 

 of extensive strata of unchanged rocks from every eruptive 

 mass, as well as from the high temperatures of the interior of 

 the earth ; sometimes they form the outermost covering of un- 

 changed mountains, and are also frequently found alternated 

 with strata, to which the metamorphic influence has not ex- 

 tended. An explanation of the metamorphosis, by the heat 

 of the adjoining rocks, or by vapours, is evidently, in this 

 case, insufficient. But that the cause of this metamorphosis, 

 whichever it may be, is more closely connected with the pro- 

 cesses of the interior of our globe, seems evident, from this 

 circumstance, that these metamorphic rocks occur in those 

 regions only which, by the up-raising of the originally hori- 

 zontal series of strata, thus forming high mountains, or by 

 tlie breaking out of eruptive rocks, bear unmistakeable 

 traces of a foimer very intense influence of forces acting from 

 the interior of the eaiih. 



Massive Rocks. 



The close connection of the greater number of metamor- 

 phic rocks with massive rocks, the perfect similarity of their 

 niineralogical character, and the gradual transition of the one 

 kind of rock into the other, lead to the conclusion that the 

 massive rocks themselves are to be considered as merely the 

 last stage of the conversion or change ; that granites also, and 

 porphyi'ies and trap-roclcs have proceeded in a similar way 

 from the original neptunian rocks, as undoubtedly is the 

 case with massive limestone, dolomite, and quartzite. From 

 this it also appears that the metamorphosis has, in individual 

 cases, proceeded as far as fluidity, which is so evident in 

 the case of granite or trap veins or dikes. In this point of 

 view, all massive rocks form a series, which begins with mar- 



