Fróðskaparrit - 01.01.1975, Page 99

Glacial Erratics
107
At greater depths than about 500 meters all cobbles have an
iron-manganese coating, less than 0.1 millimeter thick.
The cobbles are overgrown by various living organisms and
their skeletal remnants. This epifauna consists largely of bry-
ozoans and polychaetes, but silicispongiae and brachiopods
(Crania Anomalia) are common too and sometimes dominate.
The covering of epifauna diminishes with depth and is scanty
in the deepest dredge hauls (fig. 3).
That part of the surface of the cobbles which protruded
above the sea floor can be estimated by the surface weathering,
epifauna, iron-manganese coating and etch pits. On average
50 to 60 percent of the total surface of the cobbles in the
dredge hauls at greater depth than 500 meters protruded above
the sea floor. At shallower depths the average exposure of the
cobbles is more variable and it is more than 75 percent in
Fig. 2. The distribution of rock types among cobbles dredged south-
east of the Faeroe Islands.
Legend: Black = basalt, white = tuff carbonate sediments, ruled =
other sediments, stippled = metamorphic and plutonic rocks. The area of
each sector in the pie diagrams is proportional to the number of cobbles
dredged. The smallest circles correspond to 1 cobble, the largest one to
139 cobbles. Number of dredge station is shown beside the circles. Three
circles are displaced from their proper position indicated by arrows. X =
dredge hauls with no cobbles. Rock types dredged by Berthois (1969) are
shown by letters. B = basalt, S or s = sediments, M or m = meta-
morphic rocks. Upper case letters denote high relative abundance, lower
case letters denote rather low abundance. Depth contours are in meters.
2. mynd. Sundurbýtingin av grótsløgum, sum fingin vóru í landsynning
úr Føroyum.
Teknlýsing: Svart = basalt, hvítt = tuff- karbonat- legugrýti, strikur =
annaó legugrýti, prikkar = umskapað grótsløg og djúpgrýti. Víddin av
hvørjari deild í klingrumyndini er í lutfalli við tali á botngróti, sum
fingið var upp. Minsti kringurin samsvarar við 1 stein, størsti kringurin
við 139 steinar. Tølini vísa til støðirnar. X = hál har einki botngrót var
fingið upp. B = basalt, S ella s = legugrýti, M ella m = umskapað grót-
sløg vísa til Bertois (1969). Dýpdarstrikurnar vísa dýpið í m.