160 MR CUNNINGHAM ON THE GEOGNOSY OF 



Cleathel, and not more than half a mile from the latter 

 place ; indeed, on proceeding from the west to the east side 

 of the island, it is almost the first rock which presents it- 

 self. This pitchstone has a green colour, is very similar 

 to that of Arran, and contains small imbedded nodules of 

 common opal. When first fractured it is very tender ; on 

 exposure to the air, however, for a few days, it, like many 

 other rocks, acquires a greater power of resistance to the 

 hammer. Associated with this pitchstone, both trap and 

 porphyry occur, — the former of which, indeed, traverses 

 it in the form of a vein, of about four inches in breadth. The 

 nature of the ground, however, precludes the possibility of 

 making out the more intimate connections of the seve- 

 ral rocks, but from what can be seen, we are inclined to 

 believe, that the whole are of a contemporaneous forma- 

 tion. The porphyry, which is associated with the pitch- 

 stone, is identical with that which, in Arran, is connected 

 with the same rock. It in some places becomes highly 

 quartzose, and is then always encrusted with botryoidal 

 calcedony. 



Before leaving the subject of the trap-rocks of Eigg, 

 it does not appear to us irrelevant to notice the very gene- 

 ral reference of these rocks, as well as other similar masses 

 of the Hebrides, to a volcanic series instead of a Plutonic 

 group. To some it may appear a matter of little conse- 

 quence whether, since both classes are similarly produced 





ARGYLESHIRE. 





Ardnamurchan. 



In trap. 



ABERDEENSHIRE. 





Cairngorm. 



In granite. 

 LANARKSHIRE. 



MacCulloch, 



Cumberhead. 





Jameson . 



