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because the horizontality of the seismic boundaries is in con-
tradiction to the relatively large dips of the surface Tertiary
lavas. This argument involves an extrapolation of the surface
dips to depths of up to several kilometers, a procedure which
appears somewhat uncertain. In eastem Iceland, where the
dips are more regular than in other parts of the country,
Gibson (1966) has proposed an interpretation of the surface
dips, which avoids the above contradiction and supports a
stratigraphic interpretation of the 2—3 houndary.
In conclusion it can be stated that the seismic results indi-
cate that the Tertiary flood basalts form a continuous layer
all over Iceland. In the neovolcanic zone they are overlain
by younger volcanic rocks, which are usually less than one
kilometer in thickness. This is in agreement with the opinion
expressed by Einarsson (1965), that the neovolcanic zone
of Iceland is a relatively young feature, much younger than
the outpouring of the main bulk of the flood hasalts. It is
difficult to find in the upper crustal structure of Iceland a
support for a hypothesis of crustal drift or sea-floor spread-
ing, which had been going on since the beginning of the
Tertiary. Little can be said, however, ahout a possible cmstal
drift accompanying a relatively recent volcanic activity in
the neovolcanic zone.
REFERENCES
Báth, M., 1960: Crustal structure of Iceland. J. Geoph. Res. 65, 1793
-1807.
Bödvarsson, G. and G. P. L. Walker, 1964: Crustal drift in Iceland. Geo-
phys. J. R. astr. Soc., 8, 285—300.
Dagley, P., R. L. Wilson, J. M. Ade-Hall, G. P. L. Walker, S. G. Haggerty,
T. Sigurgeirsson, N. D. Watkins, P. J. Smith, J. Edwards and R. L.
Grasty, 1967: Geomagnetic polarity zones for Icelandic lavas. Na-
ture 216, 25—29.
Einarsson, Tr., 1965: Remarks on crustal structure in Iceland. Geophys.
J. R. astr. Soc., 10, 283—288.
Gibson, I. L., 1966: The crustal structure of eastern Iceland. Geophys. J.
R. astr. Soc.,12, 99—102.