Fróðskaparrit - 01.01.1975, Page 97

Glacial Erratics
105
The continental slope south-east of the Faeroe Islands slopes
very gently towards the bottom of the Faeroe-Shetland Chan-
nel at a depth of roughly 1200 meters. To the south-east of the
northern trough the average inclination of the slope between
300 and 800 meters is about but it diminishes gradually
in both directions along the slope to about 3/4° about 65 kilo-
meters to the south-west and north-east (Berthois 1969, fig. 6).
The continental slope is very regular in a longitudinal profile
and no canyons have been observed.
General descnpúon of the cohbles
The rocks in the dredge hauls have been divided into four
major groups: 1) basalts, 2) tuff carbonate sediments, 3) other
sediments and 4) metamorphic and plutonic rocks (fig. 2 and
table 1). The few pebbles retained between the cobbles in
some of the dredge hauls have been disregarded in the stone-
counts.
The size of the cobbles is limited upwards by the height of
the front opening of the dredge of only 12 centimeters. In all
the dredge hauls the mean size of the cobbles, i. e. stones larger
than 64 millimeters, only varies between 118 and 167 milli-
meters, while in the six deepest dredge hauls the mean size only
varies between 118 and 129 millimeters.
The cobbles vary widely in roundness from very angular to
well rounded (fig. 3). The majority, however, are subangular,
subrounded or angular according to the classification of Powers
(1953). This applies to all the dredge hauls. Gneisses and sand-
stones show a greater spread in roundness values than basalts
and tuff carbonate sediments, but the mean roundness of the
cobbles of these different rock types is nearly the same and
falls in or close to the subangular class. Conspicuous glacial
striae are seen on a small part of the cobbles irrespective of
rock type.
Cobbles of calcareous rocks, i.e. limestones, tuff carbonate
sediments and carbonate cemented sandstones, are usually
covered with etch pits on their exposed sides.
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