Acta naturalia Islandica - 01.02.1946, Síða 58

52
TRAUSTI EINARSSON
6. Conglomerate and breccia. At the top the stones are rounded,
but with increasing depth they become more and more angular and
increase in size and at the bottom the breccia merges into
7. a basaltic lava. There is clearly a genetic relation between the
lava and the conglomerate, the latter probably resulting from the
breaking up and weathering of the lava.
8. Many strata of brown tuff with beds of greater coarseness.
9. A coarse breccia, large boulders, somewhat worn.
10. Brownish stratified tuff.
11. Again a coarse breccia. Large boulders, very little worn, in a
grey structureless matrix (447), which consists of rounded grains
of basalt, dark glass and translucent yellow glass. I suppose this
groundmass is an erupted mud flow such as represented by the vein
(438b), which flowed over the lava (12) whose surface was already
broken up into large blocks. So the blocks were incorporated in the
mud.
13. Palagonite breccia: blocks of dark basalt in a brown matrix
and it is clear in the field that this is a primary volcanic product. A
thin section (448) of the brown matrix shows this nevertheless to
be composed of granular brown translucent glass, some grains of
opaque glass and moreover some rounded grains of ophitic olivine-
dolerite, and a few worn crystals of plagioclase. This breccia results,
it must be assumed, from the outpouring of fragmental material.
We shall lastly mention an important section near Klambrasel.
The Langavatnsheiði east of Langavatnsdalur in Þingeyj arsýsla is
a part of a volcanic plateau rising about 180 m above the floor of
Fig. 11. — Section at Klambrasel showing a dyke of coarse fragmental material.