164 GEOLOGY OF ARRAN. 



If the climber so desire, he can easily pass into Glen lorsa 

 from the head of Glen Sannox, across the col between The 

 Castles and Cior-Mhor; he will find some good plants by the 

 way, and from the top of the col reach the summit either of 

 Cior-Mhor or of The Castles without difficulty. 



A very interesting dike exists on the ridge between Glen 

 Sannox and Glen Rosa. It intersects the high southern part 

 of the ridge between the two glens, near the point where 

 North Goatfell starts up from the level of the col. The dike 

 here consists of green, or nearly black, pitchstone only ; but 

 the sides are not seen in contact with the adjoining granite, 

 nor is the dike traceable downwards into Glen Sannox. It 

 ranges, however, nearly due west across the head of Glen 

 Rosa, a little below the col, and thence right up the face of 

 Cior-Mhor, where it is found to consist of a central band of 

 green pitchstone, with six other bands, three on either sida 

 The first of these, next the pitchstone, is a quartzose claystone 

 approaching to hornstone, with light-coloured spots in the 

 base, apparently both of quartz and felspar ; to this succeeds 

 a band of hard claystone porphyry, outside of which on 

 either side is a broad band of fine-grained greenstone with 

 imbedded crystals, constituting the variety called trap 

 porphyry. The width of the vein in the first part of its 

 course cannot be determined; in the front of Cior-Mhor it 

 varies from 20 to 30 feet. The vein forms a ravine up 

 which one can clamber to the summit. Above this ravine 

 the claystone disappears, and the pitchstone central band 

 widens from 2 or 3 to 5 feet, while each of the trap bands is 

 about 4 feet. As illustrative of these curious relations, the 

 remarks in Art. 72 may be referred to. 



75. There is little else of much interest in Glen Rosa ; the 

 granite junction has been described already in our First 

 Excursion (Art. 26), and the singular chasm just noticed will 

 be seen as we pass along. The adder (Pdias bents) shown 

 in the annexed wood-cut (fig. 30) is often met with 

 in the glen, on the dry parts of the path, and in places 



