520 Se eV OGH 
about 40 per cent labradorite (about Ab,An,); and about 5 per 
cent pyrrhotite. If we leave out of consideration the olivine, 
which appears only here and there and whose age we were unable 
to determine with certainty in the present case, the hypersthene 
is the oldest mineral, as it shows an idiomorphic contour against 
all the other minerals—however, with somewhat rounded edges. 
(See the remarks in a following chapter.) 
We especially emphasize that crystals of hypersthene in several 
places have swum together to small aggregates, showing a syn- 
neusis structure (see the left side of Fig. 21), and that the hyper- 
sthene shows idiomorphic outlines also against the diallage, with 
Fic. 20.—Photomicrograph (15:1) Fic. 21.—Drawing (15:1) 
Norite from Skjekerdalen, Norway. Contains Hypersthene (in the photograph 
light gray, in the drawing lightly shaded), diallage (in the photograph darker gray, 
in the drawing dark shading), and a little brown hornblende (dotted in diagram), 
labradorite (white in the photograph, showing twin lamellae in the drawing), and some 
pyrrhotite (black). 
which, in the present case, it is not in parallel growth. This cannot 
be explained otherwise than that the hypersthene had finished 
forming before the commencement of crystallization of the diallage. 
I believe I am right in drawing the conclusion that when 
hypersthene and diallage appear together in igneous rocks, the 
hypersthene, regardless of the quantitative proportion between 
the two minerals, is prevailingly the oldest. Hypersthene (con- 
sisting of two chief components) and diallage (consisting of several 
