ANNIVEESAET ADDEESS OP THE PEESIDElfT. 89 



slate from Wicca Pool altered into fine-grained schist. However, 

 as in some of the specimens from Wicca Pool, there has sometimes 

 been little or no horizontal segregation, and the bands of different 

 mineral composition are continuous, like small deposited beds ; but 

 frequently some of these are so exclusively quartzose, and others 

 so exclusively micaceous, that I think the original differences due 

 to stratification must have been greatly increased by vertical segre- 

 gation. Even when this kind of evidence is wanting, the mutual 

 arrangement of the constituent crystals clearly shows that their 

 present outline is due to growth in situ. A portion of a spe- 

 cimen from Loch Groyle, magnified 60 linear, shown by fig. 10, 



Pig. 10. — Mica-schist of Loch Goyle, with stratification-foliation, 



3 \ 



will serve to illustrate some of the more important facts. At the 

 bottom we have a layer containing much mica, and in the centre 

 one composed more exclusively of quartz. In this layer lie large 

 and smaller plates of mica, enclosed in a number of interfering 

 crystals of quartz, which have obviously crystallized in situ round 

 them and about them. Similarly, when we examine the micaceous 

 layer, we may see that the crystals of mica also mutually interfere 

 and enclose quartz, so that the proof of crystallization in situ is 

 equally good. 



It is, however, in the case of cleavage-foliation that the proof of 

 recrystallization is the most complete ; and since the great impor- 

 tance of this structure appears to be often overlooked, it will be 

 well to consider it somewhat in detail. 



By far the best district that I have seen for studying this kind 

 of foliation is that ly'mg along the sea-coast between Aberdeen 

 and Stonehaven, especially at Portlethon, Muchals, and Skateraw. 

 At Muchals I obtained specimens which are remarkably instructive, 

 because they show in the same thin section both stratification- 

 foliation and cleavage-foHation. Pirst of all, we may see bands of 

 different mineral character showing stratification as clearly as any 

 slate, but necessarily modified by a variable amount of horizontal 

 and vertical segregation. Eoughly parallel to these thin beds lie 



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