Dr. Mac Culloch on the Vitrified Forts of Scothmd. 263 



quartz rock, and porphyry. A long mountain of trap rising at the 

 borders of Loch Etive, skirts the edges of these hills for a considera- 

 ble space, terminating on the plain of Connel by a trap breccia, that 

 pudding-stone well known to tourists as occurring in various places 

 from Connel to Oban. This breccia, where nearest the fort, is at 

 least half a mile distant from it. As the geological site of the rock 

 does not concern the present inquiry, I will limit myself to its mine- 

 ralogical description. 



It consists of rounded pebbles of different magnitudes, cemented 

 by a paste of a mixed white and brown colour. The pebbles are 

 generally small, and are much more numerous under the size of an 

 orange than above it. There are very few of considerable magni- 

 tude. They exhibit for the most part different varieties of trap, 

 or greenstone, all of which have been rounded previously to 

 their entanglement. Of these there are purple, red, gray, and 

 dark blue specimens, varying as much in solidity of texture as 

 they do in colour, and more or less homogeneous in their appear- 

 ance. Many of them are of an amygdaloidal structure, containing 

 imbedded grains of calcareous spar, zeolites, and green earth, and 

 some are perfectly cavernous and scoriform. Besides these pebbles 

 of trap, there are rounded pieces of quartz of different colours, white, 

 gray, and red, cemented in the common ground. In the specimens 

 which I examined I could not trace any other kind of rock. The 

 paste by which the whole is cemented is of a peculiar quality. It 

 is either dark purple, or brown, or mottled, or gray, or a dirty mix- 

 ture of brown, white, and dull green. It may be scratched with the 

 knife, has an earthy smell when breathed on, and effervesces with 

 nitrous acid. Its fracture is not properly granular, but rather of the 

 small splintery. Before the blow-pipe it is fused into a dark glass. 



On a minute examination it appears to consist chiefly of frag- 



