24 GRANITIC ROCKS OF OTHER COUNTRIES [Ch. III. 



CHAPTER III. 



THE GRANITIC ROCKS OF OTHER COUNTRIES COMPARED WITH 

 THOSE OF CORNWALL. 



Descriptions of these rocks neither numerous nor circumstantial. The 

 granite of Aberdeenshire characterised by its hornblende its varieties. The 

 association of granite and porphyry in the mountain Cruachan, and of 

 granite and quartz-rock near Glen Tilt. The granitic district of the 

 eastern part of Ireland, it abounds in quartz, and is characterised by 

 mica. Granitic rocks of the Erzgebirge, at Freyberg, Altenberg, and Zinn- 

 wald. Granite of the Hartz mountains also micaceous, its nature doubt- 

 ful, interstratified with schistose rocks. Remarks on the binary compounds 

 of quartz with shorl, mica, or talc. 



HAVING examined the granitic rocks of Cornwall, it is now 

 proposed to turn our attention to those of other countries, 

 in order to ascertain whether their constituent minerals are 

 similarly aggregated together ; and whether the masses re- 

 sulting therefrom are subject to the same arrangements. 

 The details, however, on this head are not so circumstantial 

 as might be desired : this deficiency is attributable to two 

 causes ; first, to the indisposition of geologists to enter 

 into mineralogical minutiae, which they have hitherto con- 

 sidered in this country to be comparatively unimportant; 

 and, secondly, to the want of such favourable opportunities 

 for investigation as occur in the cliffs of Cornwall. 



Notwithstanding the paucity of such descriptions, yet suffi- 

 cient data may be gleaned for our purpose, which is to show, 

 that the granitic rocks of other countries exhibit similar 

 variations in their mineral composition, and similar associations 

 as those of Cornwall. 



We learn, from the excellent descriptions of the primary 

 rocks of Scotland by Dr. Macculloch, that the granitic masses 

 are analogous to those of Cornwall : they have not, indeed, 

 the same composition, for hornblende, not shorl, is their 



