Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 99

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It has bulbous sides indicating penetration of soft material,
but other movement of the soft material is not indicated. On
the other hand another dyke, 2m thick, was intruded earlier
while there was still movement in the breccia layer: The
dyke was cut off and its upper part was carried 3 m south-
wards.
Mosfell and its southern foot is obviously the remnant of
a much larger mass. The section gives an insight into the
building process: we picture a slope advancing southwards.
Early there were steep tuff layers of explosive origin; then
coarser primary breccia with gentler dip was laid down and
at least partly it advanced southwards as a unity. Later,
steeper layers of primary bomb breccia were added. In the
volcanic pauses layers of scree advanced down the slope. The
brown colour of the rocks is mainly due to weathering of
the abundant glass, although this is in fact mostly of the
brown translucent type (sideromelane). All the primary ele-
ments met with here are of normal polarity.
VörðufelL
Fig. 50 shows the south side of Vörðufell. At the farm
Framnes are seen the deepest rocks (50 m above sea level),
a basalt lava of normal polarity, magnetic group nx. This is
covered by a brown conglomerate of eolian sand and river
gravel, which corresponds to the boundary between two mag-
netic groups. Over this are first two thick basalt lavas of re-
verse polarization. At 140 m they are covered by a grey
conglomerate mx on a smoothly eroded basalt floor. This is
possibly a moraine. Now come layers of kubbaberg and coarse
primary breccia (reverse polarity) and finally a thick tuff-
breccia tx reaching the edge of the slope at 280 m.
This reverse group rx occupies the slope towards the east
but is here covered by a new element, t2. Round the east
comer, above the farm Álfstadir, we get the section shown
in Fig. 51. At the base (about 70 m) we have reverse hreccia
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