Ch, V.] PRIMARY SCHISTOSE ROCKS. 65 



N. B. The general character of the upper 

 beds of granite is that of granular quartz, 

 with much silvery mica, and very little 

 felspar. 



1 2. Mica-slate is traceable in the ravine up to 

 the cattle pond, through an ascent of 

 about - 720 feet thick. 



" Some of this mica-slate contains a vast quantity of gren- 

 atite, particularly the bed marked No. 8., generally in very 

 small crystals, but sometimes in groups of large cruciform and 

 stelliform crystals, well displayed in alto relievo on the rock by 

 the wasted state of its surface." " The relations of the rocks at 

 the lead mine are equally interesting to the geologist." " The 

 whole of these alternations may be computed at one third of a 

 mile in thickness, measuring at right angles with the dip." * 



In the southern portion of this part of Ireland, granite 

 alternates in the same manner with clay-slate. " At Croghan 

 Kinshela," says Mr. Weaver, " granite supports clay-slate ; 

 and some thousand fathoms of trenches having been cut 

 down to the solid rock in quest of auriferous veins, the 

 mineral structure of this mountain has been fully disclosed. 

 The western arm and brow of the mountain consist wholly 

 of granite. The northern brow exhibits the following suc- 

 cession of rocks proceeding eastward, across the line of their 

 direction : 



1. The fundamental granite. It is composed of yellowish 

 or greyish-white felspar, grey vitreous quartz, and 

 blackish-green mica : the felspar predominating, and the 

 mica being in the smallest proportion. It is traversed by 

 veins, consisting of white quartz with a greasy lustre ; 

 and greenish-grey clay-slate, containing cavities lined 

 with quartz crystals. 



* Geol. Trans., vol. v. p. 148. et seq. 

 F 



