Rit (Vísindafélag Íslendinga) - 01.07.1962, Side 101

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as Tertiary in spite of probable glacial vestiges at a deeper
level. Below this plane we have still two magnetic groups.
The erosion horizon at 280—270 m is clearly visible along
the east side of the mountain. The base of n2 falls gently to
195 m a little north of the farm Helgastaðir after which it
drops more steeply and disappears in the low ground south
of Iða. At the same time n2 grows thicker. It consists mostly
of layers of breccia with a few layers of conglomerate, and
reaches a level of 290 m in the north end of Vörðufell where
it is covered by r2. Thus r2 covers most of the mountain as
a horizontal layer. In the north tx is mostly fine brown tuff
cut by reverse veins. On its surface rests a 10 m thick greyish
Fig. 52. A bomb, partially disintegrated during mass movement.
conglomerate which is covered by a thin layer of lignite. The
lignite is covered by kubbaberg and primary breccia at the
base of n2 and should be considered as Pliocene. The cool
climate of this time is verified by the pollen analysis made
by Pflug on material which I collected here. The picture is
closely similar to those of the Upper Plateau (Teigará, Burst-
arfell) a time prior to planation of the Plateau and erosion
of the valleys as will be discussed later (Pflug 1959).
Finally we shall go back to the section at Álfstaðir and
consider the structure of the topmost reverse group. The
thick breccia is mostly without structure. It consists of basalt
fragments with glass coating or ropy surface on one side, in
a dense matrix of glass and smaller basalt fragments. Some-
times one sees a bomb in the state of disintegration; Fig. 52
shows one example. The bomb has been crushed and the parts
are dispersing in the matrix. The matrix already surrounds
many fragments but they have not been turned, and the glass