Greinar (Vísindafélag Íslendinga) - 01.01.1976, Blaðsíða 148

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tween, on the south side, the main gullys of run-off from the
Sandfell-Mælifell pass, and a deep gully on the north side.
As the slopes of the hill are much covered with scree of coarse
blocks from the olivine-porphyritic topmost layer, and the very
contacts are hidden, we stress the fact that the underlying sedi-
ments on the bench are formed exclusively of the plagioclase-
porphyritic material from Sandfell. This shows that the olivine-
porphyritic top of the hill cannot be a plug, older than these sedi-
ments. The top-layer is what it appears to he: the remnant of a
layer resting on the unporphyritic breccia.
The latter can easily be identified as a remnant of an already
mentioned tuff-breccia layer, the unporphyritic Stangarháls tuff-
breccia.
This formed originally an extensive layer which reached the
slopes of the Skolli plain, i.a. close to Mælifell, where it forms a
remnant with a faintly eroded plain surface of 200 m height. This
breccia also forms all the surface of Stangarháls, to its northeast
end, and it forms the Lómatjarnarháls, a prolongation of the 200 m
plain at Mælifell. Originally, this layer reached the side of Bæjar-
háls, and covered the sediment in the mentioned hill farther south-
west, where it was covered by the reversely magnetized olivine-
porphyritic rock. From here to the main remnant of the unpor-
phyritic breccia at the north foot of Mælifell there is a distance of
only 300 m, and the eastward extension is at both places about the
same. Thus, we see no reason to doubt that the unporphyxitic
middle layer of the hill is an outskirt of the Stangarháls-Lóma-
tjamarháls unporphyritic sub-aquatic tuff-breccia.
This extensive layer has been cut by two broad valleys, the one
between Stangarháls and Lómatjamarháls (formed within, and a
continuation of the older valley whose east side is the Skolli plain).
The other valley was excavated between Lómatjarnarháls and
Bæjarháls, to end abruptly just southwest of the rim-off from the
Sandfell-Mælifell pass. This shows that this valley was formed by
that run-off. The existence of our hill between gullies formed by
that run-off, is most likely due to the resistance of the strong blocky
rock of reverse magnetization. That resistant cover must be older
than the valley under consideration. The valley between Stangar-
háls and Lómatjarnarháls must be considerably older than the Last