HARKER: NORWEGIAN BOULDERS IN HOLDERNESS. 3 
(IV.) Granites.—Among the granites we find less strongly 
distinctive features to warrant identification of the specimens with 
particular masses in situ; still there can be no doubt that the great 
majority of the granite boulders in the Holderness clays must be 
referred to Norwegian sources. The only British granites that we 
should naturally expect in this connection are those of Shap Fell 
and of the Cheviots; the former and apparently one variety at least 
of the latter can be recognised, but the greater number of the 
specimens belong to types widely different. Many are grey granites 
with brown mica (biotite) as a characteristic mineral; others, often 
of greenish grey colour, show both brown and silvery white micas. 
These rocks are of medium to fine texture. In thin slices they 
show bending of the micas and felspars and disturbance of the 
optical properties of the quartz, causing it to give only incomplete 
extinctions when rotated between crossed Nicol’s prisms. These 
are well-known effects of the stresses which accompany great crust- 
movements, and the granites in question doubtless formed part o 
Norw 
the gneissic areas of southern and western so find 
among the de red gra of er grain than the 
preceding, consisting essentially of flesh-coloured felspar with 
microscope shows that the felspars ar icrocline and 
microperthite ; the evidences of violent mechanical disturbance seen 
in the other granites are here wanting e of rock may be 
rather later date than the augite-syenites and rhomb-porphyries 
(V.) Gneisses and crystalline schists—Rocks belonging to these 
divisions are found among our boulders in great variety, and there 
can be no doubt as to their Scandinavian origin, but we have not 
enough information respecting the great development of crystalline 
rocks in Norway to enable us to refer individual specimens to 
precise localities. One type well represented is a banded horn- 
blende-gneiss showing lenticular white and dark streaks about half 
an inch wide, rich in felspar and in hornblende respectively. The 
quartz is partly interstitial, partly in rounded grains enclosed by the 
hornblende. Another type has the dark streaks composed largely 
of deep brown mica, with some silvery white mica in addition, the 
flakes set parallel to the general direction of banding. Another 
rock is richer in felspar and of finer texture, showing a compact 
white mass enclosing grey quartz-grains and black crystals, about 
one-fifth of an inch long, of hornblende with parallel arrangement. 
Still another type is fine-grained and dark, the most conspicuous 
Jan. 1893. 
