NOTES ON SAMPLES OF ROCKS. 371 
I. METAMORPHIC. 
(1) Phyllite and fine-grained Nodular Schist. 
The Phyllites and fine-grained nodular schists appear to pass 
into each other, indeed to be merely different stages in the meta- 
morphism of fine-grained sedementary formations. 
50. The former, as seen in this sample, is comprised almost 
wholly of mica flakes arranged in a linear manner, but scarcely 
forming foliations. They are extremely small, and are probably 
sericite. The only inclusions are minute black grains, which 
appear to be iron ore. 
34. A further stage is shown where the rock is somewhat less 
fine-grained, the mica forming narrow foliations which include 
small “eyes” of radiating mica flakes. The rock is much permeated 
by black dust-like substance. 
Among the foliations are grains of quartz arranged in places in 
a linear manner, and all more or Jess drawn out in the direction 
of foliation, so that their sections suggest a lenticular form. 
19. The composition of the nodular schist is mica, in. minute 
flakes and fibres (sericite), including much larger flakes of biotite, 
which is pleochroic in shades of yellowish brown. The biotite is 
arranged in lines indicating foliation of the rock. The only other 
constitutent of what may be spoken of as the ground-mass, are 
the plentiful grains of iron ore. 
In this mass are “spots” which, although micaceous, differ in 
so far from it that there is no trace of schistosity, and that the 
amount of biotite in them is comparatively small. 
The “spots” or “nodules” suggest, as was long ago pointed out 
by Professor Rosenbusch, that they represent portions of the rock 
substance which have been less completely metamorphosed.* 
20. A further stage is where the rock-forming mica is of larger 
size, and the rock more decidedly schistose in structure. The 
alkali mica is in comparatively long flakes, and is colourless; the 
biotite is also longer, and is darker in colour, being pleochroic in 
shades of dark brown. 
In parts there are discontinuous foliations of grains of quartz 
and mica. The “spots” are also more marked, being composed 
of distinct flakes of alkali mica, but still almost free from biotite. 
23. 25. Samples still more marked in their microscopic foliated 
structure. There are foliations of Muscovite mica and biotite or 
of these together with quartz. In places, however, the quartz is 
discontinuous, but always lengthened in the direction of foliation. 
The “eyes” in these samples are very quartzose, but as in the other 
samples are almost free from magnesia mica, 
* Die Steiger Schiefer. Strasbourg, 1877, p. 178 ef seg. Mikoskopische Physiographie der 
Massigen Gesteine, 1st part, 1895, p. 90. 
