234 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 16, 



^ 



11 





a shaft of felspar-rock covered by white and yellowish-white quartz), 

 the red rock is a hundredfold more developed in the overlying dark- 

 ^ grey and greenish schists of the 



mainland (the " gneiss " of all pre- 

 vious geological maps). In fact, the 

 schist is so permeated by the red 

 intrusive matter, that it is mostly 

 altered into a hard hornblendic flag- 

 stone ; and yet the easterly dip is 

 persistent. It is thus specially to be 

 noticed that even this striking in- 

 trusion has not destroyed the order 

 of succession ; for even here, and 

 particularly in the little bay called 

 Geo-na-vore, the quartz-rock, dip- 

 ping away at angles of about 45° 

 to the east, having been denuded, 

 is seen to be overlain conformably 

 by the dark-grey and green chloritic 

 and talcose schist, with its interca- 

 lated courses and veins of red and 

 pink felspar-rock. 

 cq | * £ Similar proofs of the intrusion of 



these red igneous rocks are visible at 

 several places between the "Whiten 

 Head on the N.N.E. and at Ben 

 Arnoboll on the S.S.W., from which 

 hill, to the ridge above Eriboll House, 

 the felspathic matter thins away into 

 the partial and evanescent layer of 

 3 feet above alluded to, and which 

 alone is detectable at rare intervals 

 in a consecutive parallel series, thou- 

 sands of feet thick. In the hill of 

 Drumtungi* (fig. 10), indeed, to the 

 east of Heilam, the igneous rock is 

 seen to intrude among the lower 

 quartz-rock, the strata of which are 

 placed in highly inclined positions ; 

 but on the east side of that hill, 

 and immediately above a little loch, 

 the limestone and quartz-rock, both dipping to the east, are con- 

 formably surmounted by regularly stratified masses of grey and 

 dark-coloured talcose schists, in which the red felspathic rocks 

 are nearly as much distributed as at the Whiten Head. This 

 occurs in Ben Arnoboll ; and on the southern side of that hill, when 



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* There is doubtless a powerful fault between the little limestone promontory 

 of Heilam and the quartz-rock of Drumtungi Hill. But such dislocations ai*e 

 quite irrespective of the general succession. 



