Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 157

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(7), (6), and (5) is a 5 m thick sediment of mudstone,
sandstone and gravel containing blocks up to 50—70
cm in diameter, well rounded. Basalt material of va-
rious types as well as rhyolite. Considerahle infillings.
(9) Very fresh primary normal breccia and a group of
light grey basalt lavas, 70—lOOm thick in Bæjarfell,
n2 or Bæjarfell normal group.
At least (1), (2), and (3) are cut hy numerous thin dykes
of rhyolite and reverse basalt. (8) marks a major uncon-
formity.
The layers (1) and (3) are clearly seen in the slope as far
as Selfjall. Above (3) are also in Selfjall mixed lavas and it
is clear that they belong to a reverse group, r3. On this rests
also here the rhyolitic breccia (5). Discordantly on these lay-
ers we have the Bæjarfell group which in Selfjall is repre-
sented by one lava forming the summit.
The base of this group lies some 50—70 m lower in Selfjall
than at Bæjargil which might correspond to an east dip of
about 1°. But it is not certain that this means a regional dip;
see below.
We have thus a group of nearly horizontal normal lavas
lying dicordantly on an erosion surface cutting the steeper
Plateau groups, and this group is older than the valley ero-
sion. At Geitá we have a 100 m thick section of the Bæjar-
fell group, containing 13—-14 lavas but hardly any sediments.
This group crops out along the west side of Geitá as far as
Hádegishnjúkar where it dives under the tuff-breccia masses.
In Strútur the group is not present. The Bæjarfell group is
considered as identical with N2 farther south.
The group rests at Geitá on about 40 m thick sediments,
well worn gravel, brown mud- and sandstone. At the base of
the sediments is coarse breccia with unworn large blocks
broken up by frost action from the underlying hasaltlava.
The torn surface is in the usual way floating in mud. The
lava is one of 3 reverse lavas seen in the lying wall.
The thick sediments are prominent in the spur between