160 GEOLOGY OF ARRAN. 



Silica, 63'70 



Alumina, 20*02 



Potash, 12-33 



Soda, 1-71 



Oxide of Iron, 1'28 



Lime, 0'89 



Magnesia, trace. 



99-93 



This analysis shews that the felspar is an orthoclase or 

 potash-felspar; and that it consists of one equivalent of 

 tersilicate of potash and three equivalents of tersilicate of 

 alumina; its formula is KOSSiO 2 + 3 (al 2 O 3 3Si0 2 ). 



We pass up by the N.E. angle of Glen Sannox, and then 

 diagonally along the back of the ridge of Suidhe- Fergus. 

 Here the whole length of the lofty ridge on the south side of 

 Glen Sannox is before us. It terminates to the left in three 

 peaks, to one of which, in advance of the others, the name 

 of Cioch-na-h'oighe is assigned height 2168 feet ; the heights 

 of the others are 2541 feet and 2687 feet, that to the south- 

 west being the highest. The long jagged ridge ends towards 

 the right in the two lofty summits of North and South 

 Goatfell. 



Ceim-na-Cailliach, or the Carlins' Step, is an immense 

 chasm or gash in the ridge, overlooked by granite walls 

 several hundred feet in height. The interior of the fissure 

 can be easily reached by entering laterally at a pretty low 

 level on the noi-th side. We find it to be merely a whin 

 dike worn down to this great depth below the containing 

 granite. The rock is a dark- coloured, fine-grained green- 

 stone of loose texture; it exhibits the concentric spheroidal 

 structure so often alluded to as characteristic of common 

 whinstone. There is no trace of any other rock; and we 

 cannot understand how it has come to be so often said that 

 this dike is pitchstone. The dike and chasm pass down into 

 Glen Sannox ; but it is very unsafe, if possible, to descend by 

 this way. The view is very wild and grand. In order to 



