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the profile Fig. 2A. Iceland with its younger basalts occupies the
middle of a gently sloping subsidence, the limbs of which are in
Greenland and on the Faroes Islands.
Therefore, the history of the Iceland region, available for study,
started in the Early Eocene hy accumulating a homogeneous forma-
tion of plateau-basalts. In all the places, where the Eocene plateau-
basalts are exposed on land, it can be easily determined that their
effusions occurred in land conditions. These conditions remained on
the area of Iceland also in the Miocene. But the underwater drilling
on the Faroes-Iceland threshold, carried out in 1974, has shown that
in this region, now covered by sea, the plateau-basalt effusions also
occurred on land.
Conclusions can be drawn accordingly that fhe first known stage
of geological history of Iceland and of the surrounding regions
consisted of plateau-basalt effusions onto the surface of the land
which existed at that time. This stage continued tmtil the end of the
Miocene. During that period enormous series of plateau-basalts were
accumulated, the thickness of which, possibly, reach 10 km. This
accumulation could occur only in conditions of subsidence of the
Earth’s crust. But the surface of plateau-basalts was always above
sea level.
Until the end of the Miocene the plateau-basalts of Iceland de-
posited horizontally. While in horizontal position they were intruded
by dikes of dolerites and diabases. Though the transition of a dike
into a basalt has nowhere been observed, it can be supposed that
the intrusion of dikes, especially numerous in the east, occurred
simultaneously with the formation of the plateau-basalts. The effu-
sions of the latter were accompanied also by central volcanic erup-
tions, the remnants of which are buried in the plateau-basalt for-
mation.
The next stage started about 9 million years ago on the verge
between the Middle and Upper Miocene. Monotonous effusion
of entirely identical plateau-basalts on the territory of Iceland
changed to considerably more variable volcanic activity. At the
same time the area of its manifestation was drastically reduced and
is now completely located within the present-day island. Volcanic
activity covered the entire major part of the island except the
North Western Peninsula and the marginal eastem region. Prob-