Acta naturalia Islandica - 01.02.1946, Page 26

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TRAUSTI EINARSSON
Fig. 2. — Section in the Palagonite Formation at Hvammur (Eyjafjöll). Total
height about 200 m. Basalt lavas, brown tuff and breccia. Further explanation
in the text.
The lowest visible horizon is a thick layer of stratified light brown
volcanic tuff and breccia (1). The layer is mostly of fine grain, but
strata of scoriae are also abundant, and rounded, worn pebbles may
be found.
The strata are undulating in such a way as to suggest the action
of wind as a dominant factor in the deposition of these sediments.
In a thin section (261) we find thatthe tuff is composed of subangu-
lar and rounded grains of translucent, rather porous glass, enclos-
ing small crystals of plagioclase and augite and a fair amount of rela-
tively large phenocrysts of the same minerals.
Besides this glass fragments we find a fair amount of separate
subangular and rounded crystals of the two minerals of the same
size as the larger group of phenocrysts, and it is clear that they are
of the same nature: broken out of the glass during the transport.
The small size of worn grains suggests again the action of wind.
The groundmass (262) of the breccia may be called identical with
the described tuff.
These layers are covered by a 2 m thick red sandstone and conglo-