Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 12

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is not a structural one. In Fig. 3 is shown the near-horizontal
plane on Ennishnjúkur cutting the more steeply dipping lavas.
Here at least a 200 m thickness of basalts is cut off by the
erosion surface in the eastern part of the mountain. A similar
observation is made in Barnadalsfjall, where the smooth ero-
sion surface cuts off more than 200 m from the dipping basalts.
In general the stratigraphic dip is markedly greater than that
of the erosion surface so that towards the east the latter cuts
deeper and deeper into the basalts. On the other hand it seems
possible that the similarity of dip has contributed to the ex-
ceptionally good preservation of the old forms in this area.
Fig. 3. Erosion surface on Ennishnjúkur, cutting the dipping
basalts.
Going eastwards from the Höfðaströnd area the remnants
of the smooth surface decrease in size. On the Eyjafjörður
side of the mountains the later dissection is very thorough and,
although the old remnants are recognizable at very many
places, they are so small and scattered that the old surface
cannot be usefully reconstructed with confidence except in
its most general features.
Finally, it should he stated that there can hardly be any
doubt that before the Older 300 m stage there was a general
peneplanation. Only after differential uplift of the pene-
planed land did the valleys begin to develop.
The ages of the erosional stages present a difficult problem.
We can attempt an estimate on the basis of the amount of
erosional work. The volume eroded during the 100 m stage
is roughly 5 times that of the later works, and corresponds
hardly to a shorter time than, say, V2 million years. The
work of the Younger 300 m stage amounts to about 10 times