Rit (Vísindafélag Íslendinga) - 01.07.1962, Blaðsíða 63

CHAPTER III.
SOUTHWESTERN AND SOUTHERN ICELAND.
The Tertiary Basalts o£ Middle Western Iceland can be
traced from the lowland of Borgarfjörður southeast towards
a line running SW—NE, as marked by Ok-Hvalfell-Súlur
-Grímmannsfell. At about this line the Plateau Basalts dive
under thick irregular heaps of basaltic tuff-hreccias and lavas.
These largely fragmental rocks I have formerly called Basic
Tuffs, but mostly they are known as the Palagonite Tuffs or
Palagonite formation.
East of the mentioned line the terrain drops suddenly,
especially in the southern part; through this displacement —
in part of several hundred meters — the Plateau Basalts dis-
appear under younger rocks. But 20—40 km farther south-
east the Plateau Basalts reappear and reach a level of 400
—600 m in the 30—40 km broad Hreppar area.
On the west side of the depression is a 50 km broad zone
of Plateau Basalts (the Borgarfjörður-Hvalfjörður block)
whose uppermost members are the Young Plateau Basalts.
In this block the lavas have mostly a dip of 5—10° SE., i.e.
towards the “graben”. But this dip is not genetically linked
with the formation of the graben; the dipping Basalts were
peneplaned before the graben existed. The latter was formed
by later movement in a narrow zone. On the east side of the
graben the Hreppar Basalts dip mostly more gently towards