L195 
group; in some slides, a.o. from the extreme northern end of rock | 
they show a zonar structure with a bordering zone of great acidity. 
Sometimes the crystals have been broken and the different fragments 
have been shifted with respect to each other, and later a greenish 
mica substance has been deposited in the cracks. The flakes of 
biotite also are often bent and show strongly undular extinctions ; 
the quartz, found in great quantity in the groundmass, shows a 
strong aggregate polarisation. The cliff on the right bank of the 
St Pakis near the rocky islands, contains rather large plagioclase 
and orthoclase erystals in the quartzose mixture of quartz, feldspar 
and biotite. Various plagioelases were determined to be andesine, 
they often show a zonar structure with more acidic bordering zone. 
Along the circumference of the feldspar crystals a granophyric 
texture is found in places. The rock contains rather much calcite, 
and also some crystals of zircon. 
The contact-metamorphic sediments alternate with numerous 
layers of granitic rocks, several similar layers — sometimes 
macroscopically, sometimes only microscopically observable, — also 
occurring in the hornfels. Thus it is a case of injection of granite 
in the schists, whereas between the stratified granitic apophyses 
the schist moreover has been feldspathised independently of the 
development of the feldspars in the granite. 
Granitie apophyses in the island II principally consist of ortho- 
clase and of, sometimes zonar, plagioclase, quartz and biotite. The 
feldspars occur as crystals of good size, more or less rounded and some- 
times strongly sericitized, enclosed by a fine-grained granular mixture 
of quartz and biotite with well marked strongly schistose structure. 
The quartz shows a strong aggregate-polarisation. Further these 
apophyses contain rather much brown or greenish brown tourmaline, 
some pyrite and a few small erystals of zircon '), which sometimes 
show rounded forms, sometimes are idiomorph, with pyramidal limita- 
tion. The hornfels differs from the granite of the apophyses with regard 
to the size of grains and the mutual relation of constituting minerals. 
They are very schistose, rich in biotite, often contain tourmaline too, 
and show a more or less distinct porphyritic structure caused by 
the large size of several of the feldspar crystals. The feldspars are 
free from inclusions, or they include a few quartzcrystals and flakes 
of biotite only. In some metamorphic rocks apatite is found in 
numerous crystals. 
1) These crystals are colourless and often show pyramidal limitation. In basal 
intersections we somelimes meet with distinct cleavage lines according to (110). 
As yel no cassiterite has been demonstrated to be present in these rocks. 
79 
Proceedings Royal Acad. Amsterdam. Vol, XVII. 
