Rit (Vísindafélag Íslendinga) - 01.07.1962, Blaðsíða 115

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220 m and a thickness of about 15 m. Below the step the sur-
face of the breccia is mainly at 110—120 m and the covering
remnants of dolerite are not more than 10—15 m thick. Far-
ther south, between Heiðará and Tílfljótsvatn, comes a still
lower block in which the hreccia surface lies at 80 m. At
Ljósafoss the thin remnant of dolerite rests on a clear mo-
raine over the breccia.
The breccia surface now maintains a constant height along
Klyfskógur to Bíldsfell and further on to the slopes of Grafn-
ingsfjöll (Húsadalur). The dolerites extend all the way.
They form a 70 m thick series in Bíldsfell and grow thicker
in Háafell and especially in Úlfljótsvatnsfjall where irregular
columnar jointing suggests one of the centres of origin. In
Bíldsfell and Háafell the dolerite is covered by further vol-
canic breccia, 60—70 m thick in Bíldsfell.
The contact of the dolerites and the covering volcanic
breccia is seen beautifully in the SE side of Bíldsfell, a few
hundred metres north of the farm Bíldsfell. The dolerite sur-
face is polished and glacially striated (S 30°E) and directly
covered with hard glacial clay, obviously left by the same
glacier that striated the surface. In places this moraine is co-
vered with separate boulders of dolerite and cobbles of an old
indurated brown tuff. Between the boulders thin laminated
clay has been deposited. It is clear that this cover of the mo-
raine is due to weathering and fluviatile transport after the
glacier had withdrawn from the place. The primary breccia
which rests on this cover is therefore not formed subglacially.
The breccia consists of fist- to head-size blocks of dense
dark basalt, often with some glass coating left, but more
usually the glass has been worn off. In addition there are
larger lumps of lava cooled in situ and these show consistent
normal magnetization, while the smaller more or less worn
blocks have no fixed magnetic direction: they had cooled
beyond the Curie point before they settled.
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