Acta naturalia Islandica - 01.02.1946, Blaðsíða 28

22
TRAUSTI EINARSSON
formation, a compact yet heavily jointed glassy mass with angular
blocks of an extremely fine-grained lava, representing a peculiar
mode of consolidation of a lava flow.
The series appears to liave been built up in a relatively short time,
without any great change of magma, and there is in particular
nothing to suggest that the alternation öf crystalline and glassy
eruptive products was parallelized by such major external events as
a radical change of climate or of sea-level. I have found nothing to
suggest that the whole series is not built up on ice-free land.
In our section there is no conglomerate which might suggest the
idea of a moraine, although such a conglomerate has been mentioned
by Pjeturss in the continuation of this series at Fit, a short distance
west of Hvammur. No striated boulders were, however, found there
by Pjeturss.
A locality with striated boulders is according to Pjeturss near
Varmahlíð, som distance east of Hvammur. But whatever the nature
of these conglomerates may be, their occurrence dos not influence
the interpretation of the section at Hvammur.
A moraine with numerous primarily striated boulders I found on
the edge of our plateau above the farm Núpur, close to Hvammur.
This moraine is younger than a heavy dissection of the plateau, but
it is older than the formation of the precipitous southern slope by
which the plateau is now cut. Now, this slope is certainly not the
work of post-glacial marine erosion, it is much older.
This shows that our plateau is of considerable age and dates at
least far back into Quaternary times.
Let us now take a more general survey of the whole series as it
is seen in the long precipitous slope of the plateau. We see that the
main character is everywhere the same as in Hvammur, from Selja-
land at the western limit, to Raufarfell some 25 km. to the east:
a pile of nearly horizontal layers of brown tuffs or breccias and
ordinary lavas. In the west the brown tuffs show a clear pre-
dominancy over lavas. In Steinafjall which is nearer to the present
centre of the complex the lavas are, on the other hand, not less
prominent than the tuffs. I could discern 5 or 6 separate layers
of brown tuff or breccia interbedded between lavas. This repeated
alternation, occurring no doubt in a relatively short period, is of
interrest as an argument against parallel major external events.