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PROF. T. Gr. BONNET ON THE 



and very distinctly schistose. The principal minerals in the former 

 are hornblende, chlorite, epidote, felspar, quartz, sphene (?), and 

 probably haematite. The rock has a somewhat foliated structure, 

 the bulk of the first three minerals being associated in rough wavy 

 lines, inosculating to form a rude network, and the interspaces being 

 occupied by felspar- or quartz-grains, across which are " trailed " 

 small insulated crystals of hornblende, epidote, or chlorite. No 

 polysynthetic twinning is exhibited by the supposed felspar, and it is 

 exceedingly difficult to distinguish some of it from quartz. The 

 constituents of the more compact rock appear to be the same, but 

 they are much smaller in size, though the hornblende-crystals are 

 sometimes larger than the rest. This mineral is not of so deep a 

 green as in the other rock. I suspect, though I have not been able 

 to prove it, that a light-coloured variety of augite is also present. 

 A rough parallelism of the constituent minerals, without much ten- 

 dency to banding, is very conspicuous. From the slide alone one 

 would have identified the rock as a hornblende-schist without hesi- 

 tation. In these specimens molecular rearrangements appear to 

 have entirely obliterated the lines of cleavage, which have remained 

 so conspicuous in the associated rocks*. 



Though I twice visited this locality, I was not able to carry my 

 examination further than the Bay of Kerselec, and then could only 

 examine the headland forming its eastern boundary from the top of 

 the cliffs, their base being washed by the sea. Its western boundary, 

 however, according to the French map, repeats the sections which I 

 have already described. 



A section on the Belon river to the south-west of Quimperle is of 

 so much interest that, although at some distance from the line 

 described above, I will briefly notice it. The new road, descending 

 to a ferry, passes over a coarse gneissoid granite, which is well ex- 

 posed on the shore below. Above the ferry-house is a fine-grained 

 mica-schist, dark grey in colour, with a marked foliation, striking 

 slightly south of west, nearly vertical, but perhaps dipping on the 

 northern side. Just below the ferry-house are several small vein- 

 like intrusions of fairly coarse granite, and further down the estuary 

 we reach the main mass of the granite. The effects of pressure on 

 the intrusive granite are very interesting. The whole has been 

 affected by cleavage-foliation. A vein, comparatively thin, and 

 lying perpendicular to the pressure, has been still further elongated ; 

 one transverse to it, or thick in section, has been distorted or zig- 

 zagged (fig. 3). The normal mica-schist or micaceous gneiss consists 

 of quartz, biotite, a white mica (in rather smaller scales), and a 

 granular mineral, probably felspar rather decomposed, with one or 

 two small garnets. It has evidently undergone compression, subse- 



* Near the most northern of the amphibolites a dyke of felspathic fine- 

 grained granite {micro -granulite, Barrois) cuts right across the strike of it and 

 the banded gneiss. It is much decomposed, contains either two felspars or 

 crystals of a felspar in a felspathic base, no great amount of quartz, and black 

 mica, some in well-developed hexagonal plates. I have not examined it with 

 the microscope. It shows no signs of being crushed. According to the map 

 this dyke occurs at intervals for about a mile along the west bank of the river. 



