Acta naturalia Islandica - 01.02.1946, Page 67

ORIGCN OF THE RASIC TUFFS OF ICELAND
61
We have triecl to make it clear that the composite plateau of North-
ern Iceland extends with a gentle dip, but without any notable break
to Southern Iceland and that the composite series at both places
are the same.
It follows from this, that the large gap in the “Basalt plateau”
right across the country which Thoroddsen assumed, and which should
be filled by the Palagonite Formation does not exist. The dislocation
of Bárðardalur does not reach far into the centre of the country, it
is already imperceptible far to the north of Kiðagil. We may also
state, although we have not considered the Eastern Fjords in this
paper, that only parts of this area are separated from the rest of the
plateau by dislocations. The composite plateau has a medium height
from Central to Eastern Iceland.
A “Palagonite Formation”, filling a major gap between blocks of
of a “Basalt Formatation” is therefore a conception which must dis-
appear from Icelandic geology.
But also the term Palagonite Formation should either disappear
or its meaning be entirely changed. In the first place there is in
principle no difference between the composite rocks of the “Pala-
gonite area” and the upper parts of the series of the “Basalt areas”.
They are only at a somewhat different level. The old distinction be-
tween Basalt and Palagonite areas must therefore be dropped in the
usual sense.
And secondly the thick masses of pyroclastic material which no
doubt are responsible for this devision into two formations, do not
only occur in the “Palagonite area” but are found also in the other
areas, e. g. Esja, Tröllafjall and Hlíðarfjall near Akureyri, and Dyr-
fjöll in Eastern Iceland.
We therefore cannot distinguish a “Palagonite Formation” in a
certain area, but instead the general picture is, that Iceland is essen-
tially a part of a larger plateau built up alternately of basaltic lavas
and basic pyroclastic material.
The disturbance of this plateau as well as the different stages of
destruction of the main layer of fragmental material in different
parts of the country are the main reasons for obscuring this simple
picture. It may be concluded that the formation of the vast masses
of pyroclastic material is in no way connected with a major sinking
of the central part of the fundamental plateau.
The Formation of the Basic Tuffs and Breccias. The observations