G4 GEOLOGY OF ARRAN. 



sedimentary deposit. The disintegration of granite, porphyry, 

 and other igneous rocks, is mainly determined by these lines 

 of separation; in some granites, but more remarkably in 

 porphyry and the trap rocks, by a concretionary structure, 

 which has resulted from the mode in which the crystalline 

 centres of affinity develop themselves at the first parting of 

 the heat of fusion, in a melted mass beginning to solidify. 

 The schistose and prismatic forms, under which granite often 

 appears, are but slight modifications of the forms already 

 noticed, depending on the relative position of the divisional 

 planes. The schistose form has often been described as a 

 true stratification ; but this structure is not continuous in 

 one direction as strata are, nor does it exhibit the fracture or 

 incurvation of beds ; it is, in truth, but a local modification 

 of the rhombic or cuboid form, under which granite more 

 frequently appears. 



31. The summit of Cior-Mhor, narrowed by distance into 

 the form of an alpine aiguille, is found to be an irregular 

 elongated plateau, large enough to accommodate a small 

 pic-nic party. The nigged shoulders flanking the peak are 

 huge rifted masses of bare rock, separated by clefts which 

 descend far into the heart of the mountain. On three sides 

 there are precipices, through clefts in some of which the top 

 may be reached ; an easy ascent is possible from the west 

 side only. Thrown forward on a salient angle of the western 

 ridge, and little more than 300 feet lower than Goatfell, 

 Cior-Mhor affords a commanding view of the ridges and 

 dividing valleys, the peaks and precipices of this singular 

 mountain group. Its situation, as the geographical centre of 

 the tract, has been noticed already, and the relations of the 

 various ridges pointed out (Art. 2). Viewed from the 

 summit, where we now stand, the scene is very wild and 

 grand. The ridges swell up steeply and nobly in front of 

 us from the very depths of the glens, in their majestic forms 

 of " peril and pride," and stretch away on either hand, 

 shooting up here and there into the highest peaks, and cut, 



