124 Dr. Mac Culloch's observations 



appear to be in their places, turn out on examination to be only- 

 large rolled stones, and these invariably consist of granite and por- 

 phyry. It is not till we have attained about two thirds of the 

 height of the mountain, that the "natural rock makes its appearance 

 in an unquestionable manner. From this part to both the summits 

 there are abundant opportunities of examination, as immense faces 

 of it are left uncovered even on the southern side where the acclivity 

 is easiest. To the north it presents a range of nearly perpendicular 

 precipices extending many hundred feet down the mountain. The 

 mass of the mountain is easily seen from this point to consist of 

 granite. This appears to be of uniform composition on both the 

 summits, and to be formed of a very equal mixture of reddish felspar 

 and white quartz with very little mica, nearly resembling the granite 

 of Cairn Gorm. The porphyry veins which traverse it are here also 

 as visible as they are below, but if there is any difference they appear 

 of greater magnitude, and the red variety predominates. There are 

 immense fissures on the northern side, which seem to have resulted 

 from the wasting of these veins. It is on the lower of the two 

 summits, as I before said, that the junction of the basaltic veins with 

 the granite is visible. 



I have remarked in a former paper* that the magnet is much 

 affected by the granite on the summit of Goatfield. This is still 

 more strikingly the case in Cruachan, its affections being indeed 

 stronger here than they are even on many of the basaltic rocks of 

 Canna. Both the porphyry veins and the granite affect it, but the 

 former in the greatest degree. Having had occasion to observe 

 these two instances of a fact but little noticed, I think it right to add, 

 that in both cases I found this property confined to the masses which 

 occupy the summits of Goatfield and Cruachan, and that I did not 

 perceive it either in the rocks or detached masses at the foot of these 



* Vol. ii, page 430. 



