BEN-NEVIS. 343 



tally for almost a mile. The beginning of the 

 line, at the east projection is accessible by climb- 

 ing up the broken rocks ; and on advancing a 

 little farther in this direction of the hollow, we 

 find it open to a splendid view of the same beautiful 

 appearance, which, along the face of the perpen- 

 dicular section, exhibits the structure of the 

 whole summit. This line of apparent junction, 

 though horizontal, is not straight, but a minute an- 

 gular zigzag ; :nd when closely inspected, is found 

 to be, not the separation of two different rocks, but 

 merely the passage of the same rock into a tlif- 

 ferent colour. For, the gradual transition of the 

 one substance into the other, with no change on 

 any of the characters, excepting the colour, de- 

 monstrates the identity and continuity of the for- 

 mation. We see it distinctly at the spot un- 

 der the north-east front of the precipice, w 7 here 

 the transition is first observed ; as the specimens 

 shew. Mr Williams, therefore, was misled by the 

 appearance, when he considered the dark- coloured 

 rock as a distinct stratification over granite : both 

 of these substances are equally massive and un- 

 stratified. * 



But as the upper part of this formation has 

 certainly an unusual and unexpected appearance, 

 in a geognostic point of view, I shall now en- 

 ter a little more particularly into the considera- 

 tion of its oryctognostic characters, for the pur- 

 pose of determining its nature and relations 



Y4 



