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as a whole, a marked linearity of craters is revealed. The
line A—B on Fig. 3 passes through or within 3 km of 17 of
the approx. 25 craters in Snæfellsnes, excluding the Snæfells-
jökull area at the head of the peninsula, which constitutes
a separate central volcano with parasitic craters. Also note-
worthy is the presence of three submerged hills on continua-
tion of line A—B, rising to within 28 m of the surface in the
bay of Breidafjördur, north of Snæfellsnes. It is not unlikely
that submarine volcanism has taken place here on the WNW-
trending Snæfellsnes volcanic line.
The Snæfellsnes volcanic zone runs perpendicular to the
main neovolcanic zone of Iceland, but coincides with a major
Tertiary dyke and fracture trend on Snæfellsnes and Vest-
firdir.
Discussion
Becent hypotheses on the building of the Icelandic basalt
plateau have advocated crustal drift by dyke injection with
tensional forces acting in an east—west direction (Bödvars-
son and Walker 1964, Gibson 1966). This view has been
opposed by Einarsson (1965) who had earlier (1963) dis-
cussed the tectonics of Iceland and recognized a biaxial stress
field in a tectonic phase of Upper Miocene or Lower Plio-
cene age, which he considers as probably connected with
the Alpine orogeny. It is now possible to look at these two
contrasting views in light of the information from western
Iceland.
A prerequisite of east—west crustal drift by dyke injection
is the presence of a large number of northerly-trending
dykes, such as are present in eastem Iceland. Dykes are ge-
nerally considered sparse on the Northwest Peninsula (Fried-
rich 1966) and trends variable. Northerly trend is dominant
in the northem part, but ENE-trending dykes dominate on
Bardaströnd and on Snæfellsnes the dyke swarms trend E
or ENE. Therefore, from what we know of dyke orientation
in Snæfellsnes in particular and in western Iceland in gene-