Greinar (Vísindafélag Íslendinga) - 01.01.1977, Side 40

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a glacial river. A small patch survives on the northern end
of Fljótsheiði as already stated, while glaciers from the high
Lambafjöll area, during such stages as would correspond to
the Older Dryas stage of late-glacial time, might not have
given it a chance of survival on the east side of Aðaldalur.
Only the Tjörnes uplift saved it there, on the top of mountains,
separated now by narrow deep valleys in the south, but as a
continuous sheet in the lower land towards the north. The
underlying normal group is seen near sealevel in the vertical
sea cliffs on the east side of Tjörnes, where it can be reached
at the lower end of a gully a few hundred metres south of
Skeiðsöxl.
There is a remnant of normally polarized lavas over our
reverse group, in Grasafjall near Búrfell (25), but if that were
to correspond to our main extensive normal group, very much
is lacking from the top basalts of Tjörnes, and exactly the basalt
marine breccia of Hvammsheiði to Húsavík is lacking. This
seems to be conclusive. But perhaps a very detailed petro-
graphic and chemical study could provide a further proof of
our linking of the main inland groups with those of Tjörnes.
Granting the correlation presented here, the Breiðavík deposits
are overlain by the reverse group of pre-glacial age, and are
thus older than the beginning of the main Pleistocene glacia-
tions, i.e. pre-glacial or Pliocene. The fauna of Breiðavík indi-
cates Upper Pliocene, so that our extensive zonal dolerite groups
would be of Upper Pliocene age.
The pre-glacial age of the Breiðavík deposits is very un-
expected, and with further surprises in store we proceed to a
discussion of the age of the main Tjörnes deposits.
The Age of the Tjörnes Deposits.
The origin of the succession of Pleistocene Ice Ages is dis-
cussed in a recent paper by the present author (26). The penin-
sula of Florida began to form as a result of long-shore drift-
ing south along the east coast of North America after the great
regression at the end of the Oligocene.