GO GEOLOGY OF ARRAN. 



perhaps, the best defined dike of this rock occurring any- 

 where in the granite of Arran. 



Two basaltic dikes occur close together, about 100 yards 

 east of the dike we have been describing; they traverse the 

 granite precipice in the same manner, but in a different 

 direction, their course being about N. 28 W. (true), subject, 

 however, to undulations. These dikes are from eighteen 

 inches to two feet broad, and are separated by a granite band 

 eight or ten feet in breadth ; elliptic masses of granite, of 

 which the largest we observed was about eighteen inches by 

 nine, are enclosed in the trap, but very little altered. The 

 alteration, indeed, is nowhere remarkable, the granite being 

 in some places coarse, in others fine-grained, along the planes 

 of contact. Specimens may be obtained of both rocks firmly 

 adhering. All the appearances point to the forcible intru- 

 sion of the trap. 



Some pretty plants occur here in shady spots on the 

 granite ledges, where a little soil has accumulated ; they will 

 reward the young botanist for his long walk to their 

 secluded habitat. The Sedum rhodiola, Oxyria reniformis, 

 Saxifraga stdlaris, Alchemilla alpina, and several others, 

 rejoice in the temperature and humidity which these heights 

 supply. 



To reach the head of the valley, and the first ascent of the 

 Pass into Glen lorsa, we now direct our steps along the base 

 of the precipice, where the grassy tufts and granite debris 

 afford a safe footing on the steep slope, keeping as high a 

 level as possible, in order to shorten the ascent by which the 

 summit is reached. As we pass along we notice several 

 dikes of pitchstone and basalt, ranging north-westwards up 

 the precipices on our left towards the summit of the ridge of 

 Ben-Tarsuin (2706 feet in height), and doubtless crossing 

 down on the other side* into Glen lorsa ; but we may not 

 now delay to trace them. The lower part of the Ben- 

 Cliabhain ridge on our right (2141 feet in height), and that 

 along which we have passed, coalesce at the head of the 



