Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 163

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5 km broad Kjalarnes, where it is cut into basalts dipping
up to 30—40°.
Here, at Kollaf jörður, we meet the extensive dolerite which
is of normal magnetization. It is quite clear that the strand-
plane existed, even much eroded, when these lavas flowed.
We see the strandplane e.g. very clearly in front of Úlfars-
fell (elevation about 60 m), cut into 5° SE dipping basalts,
where it is covered by erosional remnants of the dolerite.
This dolerite flowed in part through the low pass between
tJlfarsfell and Hafrafell, which shows how widely dissected
the Mosfell mountain group was at that time.
The position of the dolerite on the strandplane and its nor-
mal polarity place it above the lowest Pleistocene. We have
already discussed the age of the dolerite in the Kleifarvatn
area.
In the Reykjavík area high age is indicated by far-ranging
erosion. The dolerite has been wiped out on much of the
strandplane in front of tJlfarsfell. There have been some dis-
placements and this led to differential erosion. Thus in Viðey,
the dolerite is completey wiped out on a western part where
the basement goes higher than elsewhere in the close neigh-
bourhood, probably because of displacement. Finally, quite
mature valleys cut the dolerite and these are not parallel
with glacial striae in the area; they are typical river-eroded
valleys. In one of these, Fossvogur, we have inter-glacial ma-
rine sediments which prove that the valleys were practically
of present shape in the last inter-glacial. It thus seems likely
that we must demand all the Mindel-Riss inter-glacial for
the formation of the valleys.
In addition, we find quite similar valleys in the dolerite
which covers the Langahlíð. Water erosion is of minor im-
portance on these table mountains, as we saw in the case of
Geitahlíð and as is clearly demonstrated by the lack of gul-
lies. Gullies would be the first sign of water erosion and it
seems quite impossible that the more graded valleys could
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