734 J. W. JUDD ON THE SECONDAEY KOCKS OE SCOTLAND. 



and I have been told by the shepherds who frequent the mountain, 

 that such a seam of coal, two or three inches in thickness, is sometimes 

 exposed after great falls have taken place from the sandstone cliffs. 

 The surface of these sandstone strata in Beinn-y-Hattan has evi- 

 dently been subjected to subaerial denudation before the Miocene 

 basaltic lavas were poured out above them. In some cases the base 

 of the lava-streams is seen to contain numerous angular fragments 

 of the sandstone, which have been converted into a substance re- 

 sembling quartzite ; in other instances the surfaces of sandstone 

 over which the lava has flowed have been broken up into hexagonal 

 columns by the contraction of the mass in consequence of its being 

 heated and desiccated. The Cretaceous strata of Beinn-y-Hun, .like 

 those seen in the cliffs on the opposite side of Lake Arienas, probably 

 rest unconformably on Poikilitic marls, sandstones, and conglome- 

 rates ; but owing to the quantities of talus at the base of the cliffs 

 of Secondary strata, these rocks are very imperfectly exposed. The 

 outlier of Secondary strata in Beinn-y-Hun, which is capped by a 

 mass of Miocene basalts about 250 feet thick, is traversed by a 

 considerable fault with a throw of from 300 to 400 feet, which 

 appears to be parallel with the far greater fault which traverses the 

 Innimore of Ardtornish, and limits the outlier of Beinn-y-Hattan on 

 the east. 



In Beinn-y-Hattan, which rises to the height of 2308 feet above 

 the sea-level, the cap of Miocene basalts is much thicker than in 

 Beinn-y-Hun, attaining to no less than 600 or 800 feet. The series 

 of Secondary strata exposed below the basalts, too, is of far greater 

 interest in the former mountain than in the latter. The nature and 

 succession of these Secondary strata will be best illustrated by one 

 or two detailed sections obtained at points where streams have cut 

 through the masses of talus that usually obscure the cliffs formed 

 by the softer Secondary rocks lying at the base of the great basaltic 

 precipices that constitute the mountain-peak. The Secondary strata 

 lie directly upon the old gneiss rocks, and the overlying basalts are 

 evidently relics of great and wide-spreading lava-currents ; they are 

 frequently columnar, and alternate with tuffs, burnt soils, &c. The 

 Secondary strata, both in Beinn-y-Hun and Beinn-y-Hattan, are 

 traversed by numerous basaltic dykes ; one of these on the latter 

 mountain, consisting of horizontal columns, forms a very striking 

 and beautiful object. 



Section obtained at the east end of Beinn-y-Hattan, Morvsrn. 



1. Miocene basaltic lavas alternating with tuffs &c. ft. in. 



Beds of reddish-brown volcanic ash 15 to 20 



( (a) Thin seam of lignite 2 



(b) Laminated greyish clay with much carbonaceous matter 



and many obscure plant-remains 8 in. to 1 



£ cS Jji i (c) Grey chalky bed, not constant, consisting of whitish marl 

 with plant - remains, containing angular fragments of 

 the underlying Cnalk. This bed appears to afford 

 evidence of the upheaval of the marine beds before its 

 deposition to 1 6 



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