Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 134

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To the east of a narrower young tectonic zone we have
Grafningsfjöll and Ingólfsfjall. Topographically they are ol-
der than the rugged mountains in the Hengill-Vífilsfell area
but n2 and the dolerite cap of the former have their equi-
valents in the tectonically younger zone.
TIjp Pkiíeau Basalts of Hreppar and their extension
to the south and west.
In the special Map IV is shown the division of the Hrepp-
ar Basalts and breccias (with occasional rhyolites) into mag-
netic groups. These groups are termed hy r and n with run-
ing indices that are only used in a local sense.
rx is the youngest reverse group in the area. There is no
younger normal group (with the exception of post-glacial
lavas which are not considered), but the normal group on
which rx rests is called n2, and so on. rx forms a cap up to
100 m thick of lavas and primary breccias on Fossalda and
on Heljarkinn, above about 500 m elevation. The group ex-
tends north between Fossölduver and Svartá, where in the
northernmost outlier, near Svartá, it is seen to rest on the
eroded surface of n2. Towards the west it similarly forms
a cover that finally thins out and rests on n2, that forms the
Kambur area; the boundary is here just east of point 493.
n2 is a much more extensive group, consisting of lavas at
the base but kubbaberg and primary breccia higher up. It
extends from Fossalda across Fossheiði and the Ásakvísl re-
gion to Fitjaásar and at least as far north as Rjúpnafell. The
two mountains Rjúpnafell belong to a thick formation of tuff-
breccias farther north and it is uncertain whether it is a part
of n2 or forms a younger group. The decision is certainly not
easy because of lack of outcrops. From Fossölduver, n2 ex-
tends as a thin group of lavas in the SW wall of Heljarkinn,
separated from r^ by sediments containing lignite, as shown
in Fig. 66. Here we have the following succession.