EXCURSION III. 89 



probably to the state of the water in the river at the time 

 when the junction was examined. We refer to a dike of 

 greenstone which crosses the river diagonally, ranging about 

 N. 20 E., 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 north-east, 

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

 of slate range N. 65 E., or almost east and west by the 

 compass, dipping S. 25 E., 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 east side of the dike, continu- 

 ously without a change of direction. There is no mistaking 

 the rocks, both the greenstone arid slate are perfectly well 

 marked ; a portion of the former, traversed by the veins, has 

 distinct acicular crystals of white felspar, and that concentric 

 structure so peculiar to this rock. The slate is quite homo- 

 geneous a dark blue hard quartzite, in some specimens 

 resembling Lydian stone but the alteration from its ordinary 

 state is not remarkable. The principal granite vein is several 

 inches (six to eight) wide, and is traceable in the greenstone 

 through a space of fifteen or twenty yards, and runs right on 

 into the slate. Several smaller veins ramify through the 

 greenstone, dividing and then uniting again. These have the 

 structure so well described in the above extract. We con- 

 clude that the slate was first injected by the greenstone dike, 

 and that the irruption of the granite, at a subsequent period, 

 pierced through both of these rocks. The case is very 

 interesting, being the only one in Arran, that we know of, 

 in which greenstone is proved to have been erupted anterior 

 to the injection of the granite amid the strata of slate. 



46. We recommend the geologist, who is not deterred by 

 the prospect of "a pretty stiff pull," to mount at once by the 

 southern shoulder of Goatfell, avoiding the common pathway, 

 already pointed out, which presents much less to interest 

 him. He will thus have an opportunity of examining those 



