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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