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and thus refers the crust of the Iceland region to the continental
crust. We can mention again here the results of submarine drilling
on the Iceland-Faroes threshold, which showed that this threshold
in recent geological times was land, apparently, which rose high
above sea level. We shall again refer to the studies accomplished by
the marine part of the expedition, headed by G. B. Udintsev, I. P.
Kosminskaya and V. F. Kanaev on the Iceland submarine plateau
to the north of Iceland, where signs of recent land or extremely
shallow sea have been also found. Finally, it is no less important
that wherever in this region of Northern Atlantic the Tertiary
plateau-basalts were observed there are quite evident indications
of their formation on land.
The crust of Iceland, however, differs from the typically conti-
nental one by the fact that seismic velocities in it are on average
somewhat higher than under the continents: a substantial part of
the crustal section under Iceland is composed of material with velo-
cities of longitudinal waves equal to or somewhat higher than
7 km/sec. Such velocities should have belonged to continental crust,
if it were pierced by a considerable volume of heavy magmatic
material intruded from the mantle.
More than sixty years ago De Geer (9) presented a report at the
Geological Congress, where he stated that where the Northern
Atlantic is now there was earlier land, which subsided in quite
recent geological times. At present Yu. M. Sheinmann in some of
his works (37, 38, 39) has developed the same view point on the
basis of the composition of basalts of Iceland, believing that in the
history of this region tw'o stages should be distinguished: first is the
effusion of plateau-basalts on a vast area in continental conditions,
second is the fracturing and subsidence of the continental crust and
its gradual transformation into oceanic crust. This transformation
is still in progress and in the interior of Iceland rest the remnants
of rocks of a continental crust, the melting of which is connected
with the manifestations of acid magmatism; the volume of the
latter is abnormally large for a typically oceanic crust. The second
stage, which according to Sheinmann occurred in the Neogene,
coincided also with the penetration into Iceland of structure of the
mid-ocean ridge, i.e. rifts. These structures as though “ripped” the
crust already in the state of transformation.
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