Rit (Vísindafélag Íslendinga) - 01.07.1962, Side 60

60
more exceptionally, the rule being a more gradual fall of the
terrain and graded floors of the valleys.
But this is not the full story. The 100 m strandplane is
very well developed in the inner parts of Breiðafjörður, e.g.
Thórsnes, as we have seen. Its absence in the Búlandshöfði
area is therefore not a result of a sheltered position hut very
likely it is caused by tectonic movement.
We have seen that the erosion horizon at 300 m in the
Setberg peninsuia and in Grundarmön falls gradually to-
wards the NW. We also saw that this sinking is almost cer-
tainly younger than the Young sediments, and if we assume
that the sinking also postdates the 100 m strandplane stage,
the lack of this plane here is understood. We have here pro-
bably a relatively late sinking towards the Kolluáll trench
(graben?) and late movement is borne out by the intensive
volcanic activity (Snæfellsjökull volcano and the Normal
Young group).
The strandplane on the south side of the peninsula is then
a younger feature than the main 100 m strandplane, to which
Thórsnes etc. is referred, and would postdate much of the
sinking towards Kolluáll.
It now seems possible that the Young sediments in the
Búlandshöfði area were deposited at and near the flat coast
of the Younger 300 m stage. We have pointed out how the
flat Breiðafjörður area might have developed during the
strandplane stage by strandflat formation in a much dissect-
ed area. At the 300 m stage we might expect a similar deve-
lopment of a plain area in which the rivers might flow south-
wards to the Búlandshöfði area from the higher terrain in
the north. The fossils in the Young sediments would in this
way fit well with the ideas of the age of the end of the
Younger 300 m stage obtained in the Eyjafjörður study. And
the erosional work during the 100 m strandplane stage in the
Breiðafjörður area would also be comparable with what we
found in Middle Northern Iceland for such areas that were
exposed to the work of larger glacial rivers. But there are