﻿1851.] DUKE OF ARGYLL ON ARDTUN LEAF-BEDS. 



101 



that it occupied a perpendicular instead of a horizontal position in 

 the cliff, and the headland of Bourg seems to be indicated, although 

 not very clearly, as the locality. Mr. M'Quarrie, of Bunessen, to 

 whose intelligent interest I owe many of the best specimens obtained 

 from the leaf-beds, reports to me that he has coasted round the 

 headland of Bourg, and could see no such vein of tuff as that de- 

 scribed by Dr. Macculloch. 



There is one very remarkable circumstance which may serve, if not 

 to confirm, at least to strengthen the conjecture which would connect 

 the lower basalts of Ardtun with those of Staffa. So far as I am 

 aware, there is only one sheet of trap in the British Islands which 

 can be identified in point of geological age with the uppermost basalt 

 of Ardtun. That one sheet of trap is on the coast of Antrim, and it 

 bears to the columnar basalts of the Giant's Causeway the same re- 

 lation which I have supposed between the corresponding Ardtun 

 bed and the basalts of Staffa. I am indebted to the kindness of 

 James Nasmyth, Esq., of Manchester, for a minute description and 

 relative sketches of the order of the strata in that part of the coast 

 of Antrim, and for excellent specimens of the bed of charred wood, 

 which, as it will be seen, there occupies a position similar to that of 

 the leaf-beds of Ardtun. 



L The first bed (counting, as before, downwards from the sur- 

 face) is 50 feet of basalt ; the upper part being of small, the lower 

 of larger and rude columnar form. 



2. A bed of charcoal and lignite. Some specimens show the fibres 

 of the wood as perfectly as if taken fresh from a charcoal kiln. The 

 wood is dicotyledonous. 



3. Immediately under the bed of lignite succeeds a great mass 

 of amorphous basalt, precisely as in the case of the Ardtun leaf- 

 beds. 



4. Again as at Ardtun, the mass of amorphous basalt rests 

 upon a bed remarkable for the very perfect regularity of its co- 

 lumnar form. 



5 . A band of matter highly coloured with red oxide of iron suc- 

 ceeds, maintaining its position with great regularity along a great 

 part of the coast. 



6. Another bed of amorphous basalt. 



7. Another of rude columnar basalt, of a starch-like wavy form. 



8. A thin band of red oxide of iron. 



9. A very black amorphous basalt. 



10. Chalk, on which, dipping into the sea, the whole series of the 

 basaltic beds rest. 



From the top of the cliff to the chalk, these beds are no less than 

 460 feet in height. 



The amorphous and columnar basalts on which the Mull leaf-beds 

 rest may possibly not belong to the same epoch with the closely 

 similar Antrim beds ; because we have no positive proof that, like 

 the latter, they either rest upon, or have burst through chalk. The 

 flints of that formation which are found above them may be the de- 

 bris of chalk, originally deposited in the same position and subse- 



t 



