Ch. XV.] OF THE PRIMARY ROCKS. 349 



step, until the characters become perfectly legible, though 

 they may be misinterpreted. Thus, in the mountains of Ben- 

 na-vear, near Balahulish, at Loch Ranza and Loch Spey, 

 and in other parts of Scotland, described by Macculloch, 

 angular portions of various kinds of slate (as micaceous, 

 hornblende, and argillaceous schists, gneiss, and quartz-rock) 

 occur in the granite, insulated and far apart in some places, 

 and in others equalling in quantity the granite, which seems 

 only to form a connecting paste or basis ; and this again is 

 succeeded by the respective slates, in which the granite is 

 wanting excepting in the state of veins and subordinate 

 masses. 



Perhaps it may be contended that this fact indicates that 

 these slates were shattered and detached into angular portions 

 by the invasion of melted granite : admitting, however, that 

 such fragments of slate could be thus detached, and preserved 

 in insulated positions by the rapid cooling of the granite in 

 the interstices, yet, when we leave the junction of the granite 

 and slate, and proceed within the granite, numerous difficulties 

 assail us at every step. How could the small portions of slate 

 which there occur retain their accurately truncated and 

 angular forms when involved in intensely heated granite far 

 exceeding in bulk the included fragments ? By what coun- 

 teracting principle have like causes been prevented from pro- 

 ducing like effects? Why did these slates escape fusion 

 when exposed to heat equal to the melting point of granite ? 

 since one of them, the hornblende-schist, will fuse before the 

 jet of a common blowpipe; as will also the primary clay-slate, 

 if more felspathic than quartzose. Again, it may be enquired 

 how these portions of slate could have escaped the perfect 

 metamorphosis which is attributed to the most elevated tem- 

 perature ? Gneiss, this theory asserts, is more schistose and 

 distinctly stratified at a distance from the ignited mass of 

 granite, but, as it approaches thereto, it becomes more crys- 

 talline, until at last the lines of stratification are nearly ob- 

 literated, and it becomes granitic gneiss not to be distinguished 



