Rit (Vísindafélag Íslendinga) - 01.07.1962, Side 50

50
part of Breiðafjörður early in the strandplane stage, before
marine erosion at this level had proceeded far.
Farther west we enter an important area with Young fos-
siliferous rocks, whose relation to the 100 m and the 300 m
stages we must attempt to work out.
Western part of the Snœfellsnes peninsula.
The rocks of the Snæfellsnes peninsula fall naturally into
two main groups: a) “Old rocks”, or Tertiary basement, con-
sisting of basalts, rhyolites and, occasionally, gabbro intru-
sions. These rocks reach a considerahle height in most of the
peninsula but drop to about sea-level in the northwestem
part.
In the outer part of the peninsula these rocks, with their
dykes and intrusions are seen to be cut by an erosion plane.
On the south side it has a height of about 400 m from Böðvars-
holtshyrna to Breiðavík. On the north side it is at 300 m in
Grundarmön and probably is represented by the 300 m high
surfaces of the Setberg peninsula. Westwards the surface falls
to 130—150m in Kirkjufell, Stöð, Mýrarhyma, Búlands-
höfði and comes to about sea-level near Ölafsvík.
On this erosion surface, glacially striated, rest: b) The
Young rocks. These consists of 1) 40—50 m thick sediments:
moraines, gravel, sand, and clay with arctic marine molluscs,
boreal marine fauna, and interglacial flora. 2) A thick pile
of volcanic rocks: lavas, primary hreccias and tuffs. The
pile falls into two magnetic groups; the lower is of reverse
magnetization and reaches in places a height of 700—800 m.
After heavy erosion this group was covered by rocks of nor-
mal magnetization: some basalt lavas but mainly fragmental
basaltic rocks which originally reached a thickness of many
hundred metres. The lower main part of this group has been
heavily eroded. Finally there are much younger volcanic
rocks, among them postglacial lavas, especially those of the
great volcano Snæfellsjökull and its surrounding. The Young
rocks will now be studied in more detail.