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elation of these various products affords one of the most interesting 

 sections to be met with in Arran. It is best exhibited a little to 

 the west of the path which leads down from Dun-fion to the farm- 

 houses. Dun-fion, or Fingal's Fort, is the highest point on this 

 portion of the ridge, right over Corriegills shore, and 500 to 600 

 feet in height. Traces of old walls, the remains of a fortification, 

 are seen round the summit, but nothing whatever is known of 

 its history. Dun-Dhu is a prominent hill, nearly as high, a little 

 farther west, and standing out in front of the cliffs, to whose base 

 it is joined below. This hill is composed of columnar felspar por- 

 phyry ; and between it and the path descending from Dun-fion the 

 beds represented in the annexed diagram occur in a well marked 

 vertical section ; two veins of pitchstone and one of porphyry, with 

 sandstone intervening, surmounted by augitic trap. 



(a a a a) Sandstone; (b) felspar porphyry ; (c c) pitchstone; (d) overlying trap. 



The upper pitchstone vein, d, is about thirteen feet thick, and dips 

 S.W., at a small angle, probably 10 or 15, and may, therefore, be 

 conformable to the sandstone, which is seen in the quarry near the 

 footpath to dip about S.W. at 10. The rock is of a dark green 

 colour, without felspar spots, divided into beds from eight inches to 

 three feet in thickness ; and these beds consist of closely aggregated 

 prisms, or laminae splitting into prisms. The bed is very high on 

 the cliff, coming close up to the prismatic greenstone, but apparently 

 separated everywhere by altered sandstone. Its upper surface is on 

 a level with some of the depressions in the edge of the trap ridge ; 

 and, as we had repeatedly noticed a large block of pitchstone 

 imbedded in the soil on the southern slope, at the back of Dun-fion, 

 whose location there we were unable to account for, not having then 

 discovered this pitchstone vein, it appeared probable that the vein 

 might pass over the ridge. This, however, we satisfied ourselves is 

 not the case ; in searching for it a block of the Dun-Dhu porphyry 

 was found resting in a hollow of the ridge, and we conclude, there- 



