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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Dec. 5, 



It passes up into great masses of red hornstone or hardened quartzite 

 (c 1 ) mixed with fragments of limestone, and dipping very irregu- 

 larly at about 20°, to E. 10° N. A true quartzite succeeds, dipping 



Fig. 9. — Section near Loch Ailsh. 



Cnoc-Chaorinie. Alt-Ellag. 



c 1 . Quartzite. c 2 . Fucoid-beds. a. Chlorite-slate and gneiss. 

 x,p l ,p 2 . Porphyries. 



at 25°, to E. 10° S., and overlain by irregular masses of red lime- 

 stone. Red felspar-porphyry (p 1 ) follows, then quartzite, dipping 

 at 35°, and then the fucoid or slaty beds (c 2 ) intercalated with red 

 limestone and quartzite, and dipping at 43° to 30°, to E. Passing 

 over a low ridge, the next beds seen are hardened quartzite, dipping 

 at 50°, to E. 20° S. A small stream descending from the hill marks 

 a line of fault ; and beyond it beds of chlorite-slate, beautifully con- 

 torted, and resembling marbled paper on the cross-fracture, occur. 

 A second vein of red felspar-porphyry (p 2 ) follows, and then fine- 

 grained quartzose gneiss, dipping first 20°, to E., and then 40°, to 

 E. 40° S. From this point to Alt-Ellag (a distance of half a mile), 

 the rocks are fine-grained slaty gneiss in undulating beds, but the 

 dip gradually falling to 23°, 18°, and 16° at the Bridge. The same 

 fine-grained, micaceous, undulating gneiss continues down Strath 

 Oykill to Rosehall, but in all the lower part of the valley, beyond the 

 influence of the porphyry and granite on the west, has a persistent 

 N/W. strike and S.W. dip (dip 45°-50°, to S. 15°-25°W.*). 



The facts just stated leave little doubt as to the true relations of 

 the beds in this section. The only obscurity arises from the strata 

 being much concealed by soil and grass, and only visible at intervals 

 where they crop out on the surface, and, from the repeated intrusion 

 of igneous masses, modifying the usual aspect of the rocks. The 

 lower part of the section is evidently the quartzite hardened and 

 altered by contact with igneous rocks : the centre is no less plainly 

 the fucoid-beds, intermixed with some thin beds of red limestone 

 and quartzite. Over these, had the series been complete, the dark- 

 blue or grey limestone ought to have appeared, but is wanting in 

 this place ; then follows the gneiss, probably crushed out of. its do- 

 minant north-west strike in the lower Strath Oykill by the intrusion 

 of the western porphyry and granite. The remarkable change in 

 the dip on both sides of the line of junction proves the existence of 

 a fault ; but the absence of the limestone is specially fatal to the 

 opinion that there is here " conformable upward succession." This 

 absence is the more remarkable from its occurrence in full strength 

 at Elphin to the south, and also on Loch Ailsh to the north. I fol- 

 lowed the limestone along this north line till it was cut out by the 

 * See also the dips on Cunningham's map. 



