Fróðskaparrit - 01.01.1975, Page 105

Glacial Erratics
113
in the same general region. The number of erratics dredged is
not stated, but seems to be very small at most stations. All
but one of the dredge hauls south-east of the Faeroe Islands,
including four at about 400 to 600 meters depth, contain only
basalts (fig. 2). In contrast, in the dredge hauls south of the
Faeroe-Shetland Channel basalts either occur together with
sediments, metamorphic rocks and/or plutonic rocks or they
are absent. Berthois (1969) mentions no tuff carbonate sedi-
ments.
The origin of the cohbles
A probable beach gravel of local bedrock-basalt has been
recovered at station 80 at about 175 meters depth on the sub-
marine ridge making up the southern part of the Faeroe shelf.
All three cobbles recovered at this station with the Pecten
dredge and most of the small pebbles recovered simultaneously
with the tube sampler are fairly rounded and consist of a
weakly plagioclase-phyric basalt.
At most other stations, however, the cobbles are obviously
glacial erratics to judge from the mixture of varied rock types,
the presence of glacial striae on some cobbles and the wide
variation in the roundness of the cobbles.
The basalts are closely similar in petrography to the basalts
from the Faeroe Islands and there have not been found any
varieties of basalt which do not exist on land. The different
types of basalt on the Faeroe Islands occur mixed together,
but in widely varying proportions depending on the geo-
graphical position and the stratigraphical level (Rasmussen and
Noe-Nygaard 1969). The relative abundances of the different
types of basaltic cobbles fairly closely correspond to the ba-
salts in the upper series of the south-east central part of the
islands (Sandoy, southern parts of Streymoy and Eysturoy and
probably the adjacent shelf to the south-east) and therefore
we consider that the majority of the cobbles have been derived
from these areas.