Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 182

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same time, primary breccias are common in the upper groups
and this could be a genetic relationship (see below).
After a widespread tilting the Young Plateau Basalts were
peneplaned. This is very clear in Eastern and Western Ice-
land where the tilting was strongest, up to 10°. To estimate
the age of these rocks we then have the following points:
1) angular conformity with the lower Plateau basalts at
Sleggjulaakur, 2) widespread tilting (Alpine?), 3) peneplana-
tion. This suggests that the rocks are hardly younger than
± Miocene.
On this peneplane, it seems, was laid a thick general layer
of tuff-breccias, after a general glaciation of the country.
Remnants of this layer are widespread: reverse breccia of
Grímmannsfell-Kjölur and the normal main layer of Súlur;
extensive tuff-breccia masses east of the Southern lowlands
seem to belong to it. Similarly, the socle of Langjökull and
its continuation in tuff-breccia masses in the Stórisandur
area probably also is a remnant of such a layer. In the
Northeast we have the extensive normal breccia heaps of
Hólsfjöll-Axarfjörður with numerous outliers towards the
east; an outlier consisting of a thick reverse breccia forms
the higher part of Gunnólfsvíkurfjall, the result of very ex-
tensive erosion. Probable further remnants are the reverse
lava and breccia group in the Búlandshöfði area and the two
groups covering the sediments of Breiðavík in Tjömes.
As to the area south and southwest of the Thingvalla-lake
see below.
The next stage, after formation of this general layer of
fragmental rocks, was a block faulting and widespread up-
lifts forming the high terrain of today. This uplift may have
led to complete denudation of the tuff-breccia layer in wide
areas, i.e. especially in the high terrain dominated by the
Plateau basalts. But remnants of the layer are here hardly
existing except those already mentioned, so that it might be
maintained that the layer did never cover these areas. More
studies will be necessary to decide upon this question.