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one dike right up the chasm. The branches are three to four feet 

 wide; and the joint breadth, as one dike, eight or ten. The dike 

 undulates in its course from 30 to 40, conforming to the course of 

 the chasm. The chasm is, in fact, due to the dike; an original 

 depression, produced by a fault or the irruption of the dike, 

 determined the channel for the stream, and along the course of the 

 dike the water met with least resistance in its work of disintegration. 

 The chasm is nearly half a mile in length, with perpendicular walls 

 ten to fifteen in height, above which the banks rise very steeply on 

 both sides. It runs in against the great sheets of slate, forming the 

 waterfall below the mill-dam. At the base of these sheets the 

 dike is seen again, interrupted or broken off in one place by the slate, 

 from beneath which it again emerges, and appears upon the high 

 brows above in the bed of a small stream entering from the N.E. 



80. We are now at the famous junction of granite and slate close 

 to the mill-dam. The appearances have been often described ; we 

 shall quote the very clear account given by Professor Ramsay 

 (Arran, p. 4) : " The absolute junction of the two rocks is not here 

 visible; but that it is in the immediate neighbourhood, probably in 

 the bed of the dam, is clearly shown by the appearance of a granite 

 vein, about one foot broad, which penetrates the strata, and crosses 

 the bed of the stream about ten yards below the artificial wall which 

 confines the water of the dam; thus indicating its intrusion, while 

 in a state of fusion, into the stratified deposit with which it came 

 in contact. The granite is of a yellowish colour, fine-grained and 

 compact in texture, and consists principally of felspar. The slate is 

 exceedingly tortuous; and the strata are intermingled with nume- 

 rous veins of quartz of varying sizes, and which generally alternate 

 with the slaty strata in regular minute laminae." This description 

 is correct and well stated; but an important fact has escaped notice 

 altogether. It has not, indeed, been alluded to by any one of the 

 many observers who have visited this locality, owing probably to 

 the state of the water in the river at the time when this junction was 

 examined. We refer to a dike of greenstone which crosses the river 

 diagonally, ranging about 20 E. of N., and about thirty feet wide. 

 It enters the east bank of the stream under the mound or wall of the 

 dam, and is seen again on the surface, a little way toward the N.E., 

 but is soon lost under the heaps of granite blocks. The strata 

 of slate range 65 E. of N., or almost E. and W. by the compass, 

 dipping 25 E. of S., at an angle of 70. Thus the direction of the 

 dike makes an angle of 40 with that of the slate. Now, there are 

 granite veins in this dike; and these cross out into the slate on the 



