Acta naturalia Islandica - 01.02.1946, Page 16

10
TRAUSTI EINARSSON
1. PREVIOUS STUDIES ON THE BASIC TUFFS
The so-called Palagonite Formation of Iceland is a rather vaguely
defined assembly of brown or grey volcanic tuffs, breccias and con-
glomerates, which constitute a large part of Iceland. These rocks may
be dominating in one region and whole monntains are made of them,
in another layers of this material alternate with basaltic lavas.
It has been generally agreed upon that these peculiar rocks are
predominant in certain large areas of the country, viz. in an irre-
gular zone stretching across the centre of the country from NE to
SW. All the main mountains in that zone are built up of such rocks
as well as,partially, the lower ground. There is further a separate
area of palagonite tuffs, namely the peninsula of Snæfellsnes. On
both sides of the main zone lie high, heavily dissected areas of predo-
minantly basaltic plateau lavas. These enclose Middle or Lower Ter-
tiary lignite and are generally supposed to be mostly remnants of an
old basalt plateau.
There is thus in the main a “palagonite area” filling a wide gap
between the two “basalt areas”.
In the view of early workers on Icelandic geology the Palagonite
Formation was older than the Basalt Formation.
Þ. Thoroddsen on the other hand came to the opposite conclusion.
According to his opinion a central zone of the Tertiary basalt
plateau had sunk, the gap being filled by the Palagonite Formation.
In his own words: “Die álteren Geologen waren der Ansicht, dass
die Palagonitbreccie im grossen ganzen álteren Ursprungs als der
Basalt wáre, wáhrend die spáteren Untersuchungen vollstándig be-
státigt haben, dass Tuffe und Breccien junger sind, dass der sich
quer uber das Land erstreckende Brecciegiirtel spáter gebildet wurde
als das Basaltplateau, dass letzteres in der Mitte gesenkt und durch-
brochen ist, was eine grossartige vulkanische Tátigkeit veranlasste,
die wahrscheinlich fruzeitig im Pliozán begann und sich durch die
Eiszeit bis auf den heutigen Tag fortsetzt”. (Island, p. 288). And
further: “Die Unterlage (of the Palagonite Formation), die ur-
sprungliche gesenkte und zerbrochene Basaltplatte, muss sich wahr-
scheinlich unter dem ganzen Breccieterrain befinden und von den
Basaltgegenden gegen 0 und W durch terrassenförmige Briiche
getrennt sein.”