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PEOP. T. G. B0N3TEY OIT THE 



usually complete. A specimen of granite from the hillside, obtained 

 from a cutting, and so unweathered, recalls to mind some of the 

 granitoid rocks associated with the oldest Archaeans. I may add 

 that, even in the thin veins, the granite is almost as coarse as in 

 the mass, and yet the adjacent mica-schist shows no appreciable 

 alteration. 



(3) Roscoff and Morlaioo District. 



The low cliffs and skerries on the shore on the west side of 

 Boscoff, a quaint little sea-port, some sixteen miles to the north- 

 west of Morlaix, exhibit sections of great interest. The following 

 rocks occur : — (1) Banded gneiss : (2) a moderately coarse-grained 

 porphyritic granite, rather dark in colour ; (3) a rather fine-grained 

 and lighter-coloured granite ; (4) amphibolite. 



(1) This gneiss is a rather fine-grained rock, consisting (macro- 

 scopically) of quartz, felspar, and mica, chiefly black. The banding- 

 is very distinct, and is brought out in weathering, one set of layers 

 containing more quartz and less mica than the other. Thus the 

 former are paler in colour, of a yellowish or reddish-grey tint ; they 

 yield slowly and uniformly, and project in little slabs ; the latter 

 are a dull or brownish grey, they crumble away, and develop a 

 fissile structure. The annexed sketch may save a longer description 

 (fig. 4). The more quartzose layers are often rather less than 



Fig. 4. — At Roscoff. (Length about 7 feet.) 



but they are found up to 2" or 3", and occasionally more than 12" ; 

 the micaceous layers are thicker, and a micaceous streak not seldom 

 occurs in the thicker quartzose bands. They appear to pass into 

 one another, but the change is rapid. The beds are a good deal 

 twisted, but the general strike appeared to me between W.S.W. and 

 S.W., with a dip of about 60° on the southern side. There are, 

 especially in the micaceous layers, indications of a cleavage-foliation 

 coinciding with the stratification-foliation. One crag, however, 

 beautifully illustrates the independence of these structures. Here 

 a roll has brought the stratification-foliation. to make a low angle 

 with the horizon, and the cleavage can be discerned maintaining its 

 normal direction and cutting across it (see fig. 5). 



The chief constituents of these rocks are quartz, felspar, and a 



