Greinar (Vísindafélag Íslendinga) - 01.01.1977, Page 48

46
of the uplifted basalts as it can be studied from BárðardalUr
in a broad belt around the country to Esja at Reykjavík in the
south. The Northwestern peninsula is also included.
We have found three generations of valleys (33):
1) Very smooth slopes of 6—7° dip and less, formed at a base-
level about 300 m above present sea-level. These slopes are
cut by shallow valleys with a similary dipping floor.
2) Unchanged base-level, but great deepening of the valleys,
especially towards their head, so that the floor becomes flat
and broad at the mouth of the valleys.
3) Strandflat base-level, about 200 m below the earlier ones.
Only the larger valleys have become graded to the strand-
flat level, whereas the smaller ones are found in a hanging
position, with a, flat graded old floor at about 300 m height,
while the river flows in a narrow gulley between the two
levels.
The strandflat has the striking peculiarity that its devel-
opment is independent of the position, whether deep in a fjord,
as at Akureyri, or exposed to the open sea as closer to the
mouth of Eyjafjörður. Similarly the strandflat has equal devel-
opment all around the shore of Breiðifjörður, irrespective of
exposure to the open sea. This can only mean that the strand-
flat is due to decay of rocks above sea-level in a warm and
humid climate. This indicates a time of Lower Pliocene or
earlier, when the role of the length of Florida for climate in
Iceland is taken into account (26).
The morphological development in Norway is just the same as
in Iceland, as to features here of importance. According to the
studies of Ahlman, the oldest valleys on the east side of the
watershed of Norway were graded to a base-level 300 m above
present sea-level, and then we have a quite corresponding strand-
flat level. In an earlier paper (34), I tried to explain the uplift
of these countries by 200 m, especially Iceland, as an isostatic
response to the weight of the material carried away. The amount
of uplift fitted rather well, but the sudden rise in a 200 m step,
instead of a gradual uplift, was unsatisfactory and had to be