Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 78

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part of Súlur. Gagnheiði is, to be sure, made of tuff-breccias
closely similar to the main Súlur element, but the surface is
largely horizontal and no lavas equivalent to the lava series
in Fig. 34 are found. The equivalent of the superstructure of
Súlur has here most probably been destroyed by erosion. There
can hardly he doubt that when the Middle Pleistocene dole-
rites flowed, whose remnants are seen in tectonic ridges to
the southwest and northeast of Gagnheiði, (Tröllháls, and
area south of Svartagil) as well as on Ármannsfell, Gagnheiði
was not higher than the plain to the south and north. It has
since then been uplifted by about 300 m together with Ár-
mannsfell, as we shall see better below. These two mountains
are a late local uplift within the main subsidence zone.
Fig. 37. Sediments at the summit of Ármannsfell.
b — basalts; t = volcanic tuff; m = moraine.
Ármannsfell. This mountain has been divided into three
main blocks by displacements, cf. Fig. 36. It is separated from
Gagnheiði by the displacement d (about 100 m). The dis-
placements e and g are each about 50 m. All three blocks of
Ármannsfell are covered by much eroded “dolerite” lavas, of
a dense fine-porphyritic grey basalt, whicli on e-f and g-h
have eastward dip. They clearly flowed down an eastward
dipping surface on the underlying tuff-breccias.
On both sides of e the lavas are covered by erosional rem-
nants of sediments. These sediments are well seen at the top
of the escarpment on the east side of e, Fig. 37. The surface
of the lavas has first been much eroded and disintegrated by
frost into large blocks. Between the blocks, and covering them,
are horizontal layers of eolian sand and gravel. The pebbles