732 METAMORPHIC ROCKS. [Ch. XXXY. 



logical epoch, and may at some points, perhaps, have their original 

 order of position inverted. The high inclination, therefore, and the 

 quaquaversal dip of the beds around the borders of the granitic boss, 

 and the comparative horizontality of the fossiliferons strata in the 

 southern part of the island, are facts which all accord with the 

 hypothesis of a great amount of movement at that point where the 

 granite is supposed to have been thrust up bodily, and where we may 

 conceive it to have been distended laterally by the repeated injection 

 of fresh supplies of melted materials.* 



CHAPTER XXXV. 



METAMORPHIC ROCKS 



General character of metamorphic rocks — Gneiss — Hornblende-schist — Mica-schist — 

 Clay-slate — Quartzite — Chlorite-schist — Metamorphic limestone — Alphabetical list 

 and explanation of the more abundant rocks of this family — Origin of the meta- 

 morphic strata — Their stratification — Fossiliferous strata near intrusive masses 

 of granite converted into rocks identical with different members of the metamor- 

 phic series — Arguments hence derived as to the nature of plutonic action — Time 

 may enable this action to pervade denser masses — From what kinds of sedi- 

 mentary rock each variety of the metamorphic class may be derived — Certain 

 objections to the metamorphic theory considered— Partial conversion of Eocene 

 slate into gneiss. 



We have now considered three distinct classes of rocks : first, the 

 aqueous or fossiliferous; secondly, the volcanic; and, thirdly, the 

 plutonic, or granitic ; and it remains for us to examine those crys- 

 talline (or hypogene) strata to which the name of metamorphic has 

 been assigned. The last-mentioned term expresses, as before ex- 

 plained, a theoretical opinion that such strata, after having been 

 deposited from water, acquired, by the influence of heat and other 

 causes, a highly crystalline texture. They who still question this 

 opinion, may call the rocks under consideration the stratified hypo- 

 gene, or schistose hypogene formations. 



These rocks, when in their most characteristic or normal state, are 

 wholly devoid of organic remains, and contain no distinct fragments 



* For th,e geology of Arran, which I examined myself in 1836, consult the 

 works of Drs. Hutton and MacCulloch, the Memoirs of Messrs. Von Dechen and 

 Oeynhausen, that of Professor Sedgwick and Sir R. Murchison (Geol. Trans., Sec- 

 ond Series), Mr. L. A. Necker's Memoir, read to the Royal Soc. of Edin., 20th 

 April, 1840, and Prof. Ramsay's Geol. of Arran, 1841, and lastly, Mr. Bryce's GeoL 

 of Arran and Clydesdale, 3d ed. y 1864. 



