Fróðskaparrit - 01.01.1975, Page 104

112
Glacial Erratics
Metamorphic and plutonic rocks
Three quarters of the cobbles in this group consist of various
gneisses, mainly biotite gneisses. Amphibolites, mica schists and
quartzites are more rare. The plutonic rocks constitute less
than 10 percent of the cobbles and are mainly granites. No
mafic plutonic rocks are found.
The distribution of rock types
Cobbles of basalts greatly predominate on the Faeroe shelf
(fig. 2 and table 1). On the upper part of the continental slope
south-east of the Faeroe Islands the proportion of basaltic
cobbles suddenly decreases to roughly 50 percent at 400 to 700
meters depth (stations 3, 4, 8, 71, 76 and 77), while on the
opposite side of the Faeroe-Shetland Channel at 300 to 700
meters depth (stations 10, 11 and 12) between 4 and 10 per-
cent of the cobbles are still basaltic.
Tuff carbonate sediments on average constitute 7 percent
of the cobbles on the shelf and continental slope south-east of
the Faeroe Islands, but have not been found on the south-
eastern side of the Faeroe-Shetland Channel. In dredge haul 5
on the edge of the Faeroe shelf 11 out of 41 cobbles consist of
variable tuff carbonate sediments.
Cobbles of »other sediments« and »metamorphic and piu-
tonic rocks« greatly predominate on the south-eastern side of
the Faeroe-Shetland Channel, and they make up about 45
percent of the cobbles on the north-western side of the channel
at 400 to 700 meters depth. The proportion of »other sedi-
ments« to »metamorphic and plutonic rocks« is about 7 to 2
from the stations on the south-eastern side of the channel, but
about 2 to 1 on the north-western side of the channel, whereas
the relative abundances of the various types of sandstones are
roughly the same on both sides of the channel.
This broad distribution of rock types is similar to that de-
scribed by Berthois (1969), who has made several dredge hauls