114 ' PEOCEELINGS OF THE GEOLOGICAL SOCIETY. [June 9, 



instances to the S.E., more often to the N.W.; and that in one 

 stratum Qi) two cleavages occur, one in each direction. The strike 

 of the cleavage, on the other hand, is very constant, from E. 10° or 

 15° N. toW. 10° or 15° S., — ^the chief exception being in c, where it 

 is W. 30° N., thus diverging ftdl 40° from the others. 



The average strike of the cleavage also varies fully 20° from that 

 of the beds. It comes within 15° of the strike observed at Easdale, 

 but, on the other hand, is nearly at right angles to that at 

 Ballahulish*. On comparing the strike of the cleavage with the 

 position of the great overlying masses of trap-rock in Mull and 

 Lorn, no very intimate relation can be discovered. The Lorn trap, 

 which is nearest, Hes, in the case of Easdale, chiefly on the north- 

 east ; in that of Oban, on the south-east. On the other hand, both 

 the direction of the strata and the strike of the cleavage have 

 evidently a most intimate connexion with those far more ancient 

 and deep-seated causes which have produced the most striking 

 features in the present physical configuration of the country. They 

 are nearly parallel, for instance, to the shores of the Linnhe Loch, 

 to the Island of Lismore, and to the great depressions occupied by 

 Loch Etive, Loch Awe, and Loch Eyne. 



Trap-veins of Easdale and Oban. — Another remarkable feature 

 of this locality is the great abundance of veins of trap. Being 

 harder and less destructible than the rocks which they inter- 

 sect, they often remain projecting beyond them, like ruined walls. 

 Such trap-veins are common on the coast of Seil; and a very 

 picturesque one may be seen near the bridge connecting that 

 island with the mainland, built up of rude horizontal columns 

 and overhung with ivy and wild flowers. In one visit to Eas- 

 dale, I enumerated more than a dozen trap-veins on that small 

 island alone ; but there are many more ; and, were the neigh- 

 bouring part of Seil included, the number might be very greatly 

 increased. Erom the manner in which they intersect, they are 

 evidently of diverse age. Thus one vein of porphyritic basalt, 

 on Seil, runs partly through the slate, partly through a kind of 

 tufa-rock, and is, in its turn, intersected by another vein of blue- 

 coloured amygdaloid. Here, therefore, we have trap-rocks of three 

 periods at least. One set of veins, running generally parallel to the 

 slates (and to which my attention was directed by Mr. White), are 

 apparently the oldest, being intersected by all the others. These 

 consist of an amygdaloidal claystone, containing many small round 

 nodules of calc-spar. Its colour is ash-grey, with a slight tinge of 



* It may be necessary to mention that the Une drawn on the Map which 

 accompanies the very ingenious memoir of Mr. D. Sharpe, " on the Foliation and 

 Cleavage of the Eocks in the North of Scotland" (Trans. Eoy. Soc. 1852, p. 445), 

 represents apparently the position of the mineral masses as laid down on Dr. 

 Macculloch's Map, and not the cleavage-planes, which are beautifully seen in the 

 principal quarry, dipping W. by compass, and thus nearly at right angles to that 

 line. I intended to have given an account of the slate-rocks of Ballahulish in 

 this paper ; but, although I have made three visits to that locality in different 

 years, I have not been able to satisfy myself as to the exact relations of the rocks 

 in that highly disturbed region. 



