318 Correspondence. 
stretching. The bowlder forms are sometimes completely flattened. 
Like others, he traces a connection between these actions and fissility 
in the rocks. The banded arrangement of the mica in certain gneissic 
rocks he regards as an effect of stretching; and this, he says, is often 
independent of the dip. Not unfrequently a gneiss and the conglom- 
erate bedded in it are both stretched in the same direction, thus mak- 
ing it evident that the gneiss assumed to be stretched is really 
stretched. As a result of pressure certain granitic rocks assume the 
condition described as gneiss granite and porphyritic gneiss. The 
stretching phenomena have a direction parallel with the axes of the 
great and small folds resulting from orogenic efforts, and hence the 
author concludes, perhaps too readily, that the small folds and 
crumplings of the rocks are also an effect of stretching. But the par- 
allelism of the stretching direction and the folding axes may have only 
a coincident, not a causal, relation. The orogenic disturbance of the 
Scandinavian peninsula is thought to constitute, with that of the 
British Islands, a single system, only interrupted by the subsidence 
of the area of the German ocean. 
It is not important to notice here the distribution of the geological 
features of the region described ; nor to refer specifically to the differ- 
ent petrographic features brought into view. A few points of unusual 
interest may, however, be mentioned. A large development occurs on 
the Bommelo (island) — partly described lieretofore as saussurite- 
gabbro — in which the evidence is that the hornblende is an aucient 
augite altered into uralite— kernels of diallage sometimes remaining. 
An associated rock is a quartz-porphyry tuff — in older descriptions 
called hornstone porphyry or quartzite, composed mostly of sharp- 
edged fragments, and evidently clastic in nature. This in other places 
becomes an obscure mixture of quartz and feldspar, with a granitic 
appearance. The rocks in this region are traversed by altered diabase 
dikes of various ages. Younger than these are auriferous quartz veins. 
Of the dikes mentioned, some are called "slate dikes." They are 
dike-formed masses consisting of a soft schist whose dominant compo- 
nents are chlorite and calcite or dolomite. These are considered 
altered diabase dikes. The diorite shows some interesting passages 
into schists. Along the boundary line between the diorite and the 
quartz-jiorphyry, the former becomes fissile. In approaching the 
boundary it is seen to contain chlorite laminae which divide it into 
lenses. Closer to the boundary these increase in number, and the 
diorite becomes more and more slaty till it passes into a wholly 
chloritic schist. 
The clay-slate, somewhat to the northwest of the granitoid rocks, on 
islands near the coast, is shown under the microscope, to be wholly 
crystalline, consisting of fine-grained quartz, feldspar and muscovite 
with occasional calcite, and sometimes graduating into muscovite 
schist. 
On the eastern shore of the Bommelo is a peculiar rock. It is a 
granular crystalline, gray granitic rock, stained with dark spots, 
