476 Dr. Mac Culloch on Ouartz Rock. 



instances, a connexion In structure and habits Is established betweeri 

 certain rocks of the primary and of the secondary classes. In all 

 cases the mica Is disposed In lamellae parallel to the strata or lamlnse 

 of the rock ; it Is never as In gneiss partially disposed In different 

 directions, still less as In granite Indifferently placed. This rock Is 

 succeeded by quartz rock In large masses. Some beds of a hard or 

 compact schlstus, of a character often approximating to hornblende 

 slate, are also found to all appearance alternating with it, and I 

 have already noticed In the paper above alluded to,* that granite 

 veins are found to traverse this particular sclilst. The hill Is, on Its 

 accessible face, so covered with soil, that no very positive evidence 

 can easily be procured of the alternation which I suspect ; and the 

 precipitous faces are generally Inaccessible, always hazardous of 

 access. As we approach the summit of the mountain, the quartz 

 rock becomes established to the exclusion of the schist, and It con- 

 tinues to the top, where it offers that aspect of complete disinte- 

 gration before described under the heads of Jura and Assynt, which 

 covers the tops of the quartz mountains with ruins, and gives them 

 that acute apex and regularly conoldal declivity, which, as far as I 

 have yet observed in Scotland, Is sufEcIent even at a distance to in- 

 dicate the nature of the rock of which they are composed. The 

 laminated or stratified structure Is by no means so evident In this ex- 

 ample as In those I have before adduced from Jura, Schlhalllen, 

 and Assynt ; but It still bears the marks of a broken and disturbed 

 stratification. Such being the case, and such the Infinite variety of 

 position, direction, and elevation, assumed by this rock, I think it 

 unnecessary to enter into any details on these heads. I may only 

 remark generally, that It stands at an angle not far deviating from 



* Vide paper on Cruachan. 



