Rit (Vísindafélag Íslendinga) - 01.07.1962, Blaðsíða 107

105
tain. These lavas rest immediatly on the breccia layers in
a similar way as in Bláfell; the lavas have been the final vol-
canic product, flowing over a delta-like layer of tuff-hreccias.
At Tannastaðir the dipping layers rest directly on horizontal
layers at about 200 m. The breccia has advanced in a southern
direction over a plain surface. The mechanism of advancement
recalls that of foreset beds in a delta, and the conclusion can
hardly be escaped that the similarity is more than apparent.
One does find occasional layers (in IV and V in Fig. 54) that
might be called conglomerates, in which the basalt blocks
are considerably worn.
The northem part of the west side of Ingólfsfjall is shown
in Fig. 56. From Hvammsgil the horizontal erosion horizon
on the reverse breccia rx is clearly visible as far as Kallbakur.
The breccia is here represented by a primary but consider-
ably transported tuff, traversed by several reverse dykes or
veins (90—170 m) as was the case in the north part of Vörðu-
fell. The uppermost 20 m though are a coarse primary breccia
and lava tongues. On the plain erosion surface rests a suc-
cession of finer and coarser horizontal sand layers, essentially
of eolian origin but ending with essentially primary tuff-
breccia. These layers are in part like flows of glass fragments
and glass is on the whole very prominent.
On this rests at 210 m a 65 m thick primary very coarse
mass b^ of a quite different appearance and origin. It is a
crumbling flowing lava, a coarse breccia in statu nascendi.
Here and there are larger compact lava masses, then there are
such lava masses that are seen to be breaking up and spread-
ing, just as we saw earlier in the case of bombs. Then there
is a matrix of angular blocks from larger ones down to finer
debris. The matrix of finer debris has been squeezed into the
fractures of the disintegrating masses and it was in this fluid
matrix that the fragments flowed apart.
Some basalt fragments have glass coatings and considerable
glass flour is part of the matrix. The basalt fragments have
always normal polarity and the same is true for the finer