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10
GEOLOGICAL MEMOIRS.
internal structure and mineral contents ; since the former of these
varieties was seldom found to contain extraneous minerals, whereas
the latter was generally rich in such.
With regard to the first of these classes, reference can be made to
the paper itself, with its illustrations *, from which it would appear
that this granite shows itself in veins of all sizes, cutting through, or
imbedding itself in, the gneiss, and generally possessing a much finer
grain and more confused development than the other variety.
The second class is treated more in detail, as being particularly
favourable to the development of extraneous minerals. The first
symptoms of the appearance of such granite seem to be where there
is seen here and there in the crystalline schists small nodules of
white quartz, of reddish-grey orthoklase, or of yellowish-white oligo-
klase, of a greater size than the particles composing the rock itself.
Still further developed, as can be seen at Gronholmen, Flougsta-
doen, &c., these nodules are composed of one or both species of fel-
spar, along with quartz and mica, in particles varying in bulk up to
the size of the fist ; the laminae of the gneiss bend round the nodules,
like the woody fibre surrounding a knot in timber.
When the size of these nodules increased, it was found that the
particles of their constituent minerals also became larger, less inter-
mixed with each other, and of better crystalline development ; and
further, that extraneous minerals were found more frequently present
in proportion to such increase of size.
The appearances presented by such granitic masses, with their
progressive development, will be better seen from a few of the illus-
trations which are here subjoined.
Fig. 1 is a horizontal plan of part of an irregular granitic mass in
Fig. 1 . — Ground-plan of a granitic mass, ivith quartz-nodules, in
gneiss at Kalvesund.
the gneiss at Kalvesund. Lenticular masses of quartz (a, a) are
here seen surrounded by a mixture of orthoklase and mica.
At Flougstadoen also is seen a similar case (fig. 2), where a
nodule of quartz (« «) is surrounded by a mixture of the same com-

• In Plate III., Norske Mag. f. N. vol. viii. part 3 ; some of the figures of which