56 GEOLOGY OF ARRAN. 



headlong across the huge granite sheets in a series of striking 

 falls. The junction has not been so well shewn these few 

 Tears as it was formerly, iu consequence of the accumulation 

 of loose masses of granite; still it is sufficiently well seen to 

 make the place interesting and instructive in a high degree, 

 and some future floods in the river may again open it better up. 

 The slate is greatly altered for a considerable distance down 

 the stream, and pervaded by small veins and strings of quartz, 

 and granite in which quartz predominates. The colour of 

 the slate is changed, having more of blue than is usual to it ; 

 the structure is altered also, the laminae are contorted, and 

 present thin bands of different colours, chiefly blue and gray; 

 the latter being purely siliceous, that is, flinty slate or 

 quartzite without the colouring matter, iron or manganese, 

 which exists in the former. The slate on this side of the 

 mountains is generally a dark-coloured, coarse, siliceous rock, 

 shewing shining crystalline flakes in fresh fractures; in some 

 places assuming that arenaceous, semi-conglomerate structure 

 which used to be designated as greywacke. Both structures 

 are obliterated on approaching the granite; the colour is 

 bluish, or blue and gray in alternate bands, the structure is 

 extremely fine-grained, and the hardness and toughness are 

 both excessive. These changes, the contortion of the laminae, 

 or the total disappearance of all stratification, coupled with 

 other modifications not seen here, but to be again noticed, 

 clearly indicate that the schist to a considerable distance 

 from the granite was subjected to intense heat, and remained 

 in such a state of at least semi-fusion as to permit, under the 

 action of chemical forces, a new arrangement of parts, and 

 the permeation and interlacing of veins from the fluid 

 mass below. The granite veins are less numerous, smaller, 

 and of varieties differing from the ordinary type of this rock 

 more than is usual in most other junctions with the slate ; 

 such might perhaps be seen in the interval of several yards 

 here obscured before the granite itself is reached. The great 

 extent of the altered slate seems to indicate that the strata 



