Rit (Vísindafélag Íslendinga) - 01.07.1962, Síða 103

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by coalescence of the small bubbles during flow (cf. Einars-
son 1949)d)
Some 80 m south of the outcrop shown in Fig. 53, we have
again a primary breccia containing disintegrating bombs.
From the dipping layers we have described the same pro-
cess as at Mosfell is evident: advance of a slope towards
the south. Conditions are not clear in the northern part of
Vörðufell but at one place slight indication of northward dip
in r2 was seen. The origin of this layer may therefore pos-
sibly have been within the present area of the mountain,
and some superstructure may have been lost by erosion.
On the southern edge of Vörðufell the topmost primary
breccia rests at about 320 m on finer, horizontally stratified
tuff. A vertical reverse dyke here cuts the tuff and the breccia.
The tuff is partly volcanic but there are also such eolian sedi-
ments as the breccia rests on above Álfstaðir, and at the bot-
tom is the moraine which rests on the lower mass of reverse
tuff-breccia at 280 m. The normally polarized group is ab-
sent here.
Ingólfsfjall.
In the low ground between ölfusá river and the southeast
part of Ingólfsfjall Plateau Basalts of reverse polarity and
with a west dip of 6—7° are seen. This can be considered as
a part of an old erosion surface on Tertiary basalts. On this,
closer to the mountain, is an erosional remnant of a primary
red-brown breccia and irregularly columnar masses of nor-
mal polarity. This should probably be considered as the low-
est member of the Ingólfsfjall rocks but an unbroken con-
nection with the mountain is not seen.
J) In a submarine volcanic breccia near Húsavík, N-Iceland, the bombs
are similarly mostly dense and I have assumed (in manuscript) that this
is so because the extemal pressure did not fall long enough to atmosphe-
ric pressure during the eruption.