HORN BLENDE-SCHISTS, GNEISSES, ETC. OF SAEK. 



133 



from which the granitic bands above mentioned have proceeded, 

 or is it distinct from them ? The difference between the two 

 rocks is not great, and the fact that this brecciated mass, on 

 both sides of the island, appears commonly to occur immediately 

 above the basement- gneiss might be urged in favour of the former 

 thesis. At the same time we occasionally met with masses of the 

 coarse hornblende-rock at considerable distances from the basement- 

 gneiss, both in the normal hornblende-schist and in the banded 

 gneiss, and we found it, as already said, almost impossible to draw 

 any definite line of separation between these two rocks and the 

 distinctly brecciated parts. 



Pig. 5. — Relations of granitoid and gneissoid hands to hornblende- 

 rock in Port a la Jument. 



X Fragments (in places passing into streaks) of hornblende-rock. 

 A to B measures 15 inches. 



The evidence in the sections described above was not to our minds 

 conclusive. At the same time the basement-gneiss seemed always 

 to maintain a character of its own, to be sometimes distinct from 

 the overlying rock, and to suggest at others a slight fusion or 

 confusion of its upper surface with that rock, such as might 

 occur during an intrusion under exceptional circumstances, rather 

 than an identity with the granitic or gneissic veins. These 

 also, where they are most distinctly veins and most granitic in 

 character, are aplites (as has been said), considerably lighter in 

 colour and poorer in mica than the basement-gneiss. Moreover the 

 basement-gneiss occasionally (as in Port du Moulin just north of the 

 path leading to the shore) contains included masses which closely 

 resemble the hornblende-schist. Again, once or twice south of Port 



and felspar, which, as has been so often pointed out bj one of the Authors, 

 differ, in the absence of idiomorphic crystals and in their peculiar outlines, 

 from those in ordinary holocrystalline igneous rocks. The brecciated aspect of 

 the hornblende-rock may be due to a shattering of the mass at the time 

 of the intrusion, and a certain amount of mineral change in the outer, more 

 disturbed, and more heated portions. 



