Fróðskaparrit - 01.01.1975, Blaðsíða 108

116
Glacial Erratics
It is not likely either that the sudden decrease in the pro-
portion of foreign erratics is due to the stranding of icebergs
along a former coast. The deepest dredge haul dominated by
basalt is number 721) at about 280 meters depth; this is much
too deep for a strandline from the last glacial epoch. Because
the Faeroe Islands are sinking slowly (Jessen and Rasmussen
1922, Jessen 1925) the strandline could possibly be from an
earlier glacial epoch, but then again we should not expect to
find any evidence of such an old strandline by dredging.
The few foreign erratics found on the shelf (about 4 percent)
suggest that the Faeroese ice sheet covered the shelf during
nearly all the last glacial epoch. In addition, the glacier front
seems to have been stationary for a long time as the minimum
distance between stations with close to 100 percent basalt and
stations with about 50 percent basalt is only 10 kilometers
(fig- 2).
The majority of the basaltic erratics on the shelf and slope
were probably derived from the south-east central part of the
Faeroe Islands, as mentioned earlier, and this suggests that the
ice was moving. However, the high abundance of foreign
erratics close to the glacier front suggests that the Faeroese
ice sheet was less productive than the ice sheet on the south-
eastern side of the Faeroe-Shetland Channel. This points to a
rather small thickness for the ice on the shelf south-east of the
Faeroe Islands. If the ice was not much thicker than the present
water depth there should not have been any appreciable glacio-
isostatic uplift of the shelf, and this may explain why we
apparently find very slightly weathered beach gravel at about
175 meters depth at station 80 in the southern corner of the
shelf.
We have mentioned earlier that the two troughs on the shelf
*) Dredge haul 72 contains 5 cobbles of basalt, and besides 19 pebbles
of basalt, 1 pebble of tuff carbonate sediment and 1 pebble of sandstone.
Dredge haul 75 and four dredge hauls made by Berthois (1969) are deeper
and contain basalts only, but it is uncertain whether they are representive
because the number of cobbles is either very small or unstated.