PBESSUEE m STEATIFIED PALiEOZOIC BOCKS. 13 



which vary from 60° to nearly 80°. In this case also I believe the 

 flakes are in the general direction of the original bedding. 



I found a similar double structure in slates which I have examined 

 from the Torcross district, and from other localities where the roclis 

 have undergone exceptional folding, the result presumably of excep- 

 tional pressure ; but it is by no means present in all slates. One 

 specimen from Torcross does not show it, others do. 



The question then arises, Is this incipient foliation in any way 

 connected with contact-metamorphism? In several of the cases which 

 I have examined from other localities there is not the slightest 

 reason to suspect the presence of any igneous rock. It is true that 

 in the example just described the crag exhibits at no great distance 

 two dykes of felstone or micro-granulite, each about 4 or 5 feet 

 thick. These, however, produce little appreciable alteration in the 

 slate with which they are in contact. It is veri/ slightly indurated, 

 but its colour is unchanged. Moreover I have examined a junction 

 specimen microscopically. The mica flakes are very slightly larger 

 and a little more clearly separated from the quartz than in the other 

 specimen, but the diff'erence is hardly more than may be seen in some 

 parts of the latter, while one or two little bits of slate, actually 

 included in the igneous rock, are practically unaltered *. The slate 

 also shows strain-slip cleavage, the planes of which are abruptly 

 crossed by the igneous rock, and obviously existed prior to its 

 intrusion. There can, then, be no doubt that these dykes have 

 nothing to do with the incipient foliation. Possibly, however, 

 tiny flakes of mica may have been, from the first, important 

 constituents of the rock ? No doubt flakes of mica frequently enter 

 into the composition of muds which are subsequently converted into 

 slates, but, after a very careful study of these and other specimens, 

 I am forced to conclude that here the mica has not the usual 

 appearance of fragmental scales, but appears to have been developed 

 in situ. To this subject I shall have to return ; for the present it 

 will sufiice to have established that the incipient foliation and the 

 strain-slip cleavage were anterior to the intrusion of the dykes, and 

 in no way connected with contact-metamorphism. 



Let us now examine some specimens from the south of Morlaix, 

 where intrusions of granite are common and indubitably affect the 

 adjacent rocks. I collected a series from a partially quarried crag 

 at a distance of 8^ kil. on the Huelgoat road. They occur thus, 

 enumerated in descending order : — (] ) Banded micaceous schist ; 

 (2) Dull grey quartzite ; (3) Banded micaceous schist, like (1), but 

 looking rather more altered, and in some places containing a mineral 

 resembling andalusite; (4) Eather silvery micaceous rock with 

 imperfectly developed prisms or oval spots of a similar mineral, 

 generally lying parallel with the surface of apparent foliation; 

 (5) A dark brownish somewhat spotted and somewhat micaceous 

 rock, not definitely foliated. The quartzite was much the thinnest 



* The rock (at the margin) is a micro-porphyritic quartz-felsite. The way 

 iu which it has been "injected" into cracks in the slaty rock shows that it 

 must have then been quite in a fluid condition. 



