Greinar (Vísindafélag Íslendinga) - 01.01.1977, Blaðsíða 69

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tion of very deep burial. Broadly speaking, we can state: the
older an outcropping rock is, the deeper and longer it is likely
to have been buried and the more its original properties may
have changed.
Is it then really surprising that when we get down to the
early Tertiary and beyond, i.e. study rocks which in most cases
must have been rather deeply buried for a long time, we find
that one more of their properties has changed?
We refer to the fact that rock magnetization becomes so irre-
gular in the lowest Tertiary and older rocks, that it cannot be
explained by a global dipole field — unless whole continents
be transported for such distances as 5000 km, rotated or twist-
ed. In this procedure there is no reference to a natural cause
of the movement, the criterion just being a tolerable agree-
ment with a dipole field, which can nearly always be acquired
in this way.
But there are serious doubts, whether at all there should
be an agreement with a dipole field. Is it realistic to postulate
that magnetization is a property which is exempt from the
increasing vicissitudes to which rocks are subjected by increas-
ing burial and age?
Here is a rule giving the reason, why one would just expect
disorder in paleomagnetism with age and increase of depth of
burial and hydrothermal alterations. But to our knowledge,
there is no fundamental reason, why continents should have
begun to drift apart in about the Jurassic. On the contrary, one
finds significant evidences for unehanged positions of the con-
tinents since much earlier times. Ignoring this, paleomagnetic
evidence of the nature of disorder has been used to revive an
already much discussed and abandoned theory of continental
drift.
In 1957 (47) the present author pointed out that for sedi-
ments in Britain one finds a declination aligned with the known
tectonic trends: the Caledonoid trend (Triassic, Lower Car-
boniferous, and Old Red material), the Malvernoid trend (Old
Red, and Cambrian material), and the Charnoid trend (Torre-
donian material). And in Arizona one finds similarly the Sierra