Rit (Vísindafélag Íslendinga) - 01.07.1962, Side 144

taining vestiges of cold climate and even glaciations in some
cases. In addition there is the group rx of Heljarkinn which
may be younger than the tilting and planation of the Plateau
but is on the other hand older than the valley erosion in the
area. With NUl5 this adds up to 7 magnetic groups.
The relative position of Vörðufell may now be considered.
It is perhaps not excluded that rx here corresponds to the
Plateau group r2. But as the latter as well as the Gullfoss
group are tilted in this area while the Vörðufell groups, at
least above n1; are horizontal, it seems more likely that Vörðu-
fell is younger the the Plateau group n2. rx in Vörðufell
might rather correspond to rx in Heljarkinn. If this is cor-
rect we may add rl5 n2, and r2 in Vörðufell, as well as NU1?
to the 5 Plateau groups. Thus at least 9 magnetic groups
overlie the lowest glacial vestiges in Hreppar.
It is not possible to trace the groups in Hreppar northwards
across the country. But the very similar position of the upper-
most Hreppar groups and the groups we have studied on the
north side of the highlands makes it highly probable that
these are identical.
The thickness of the Young Plateau Basalts is considerably
greater in Hreppar than in Northern Iceland. This may
mean that the volcanic activity began that early to concen-
trate in a subsiding southern area.
Mosfellssveit—Skálafell—Kjölur.
To the south of Esja is a cluster of rather low mountains
which we shall call Mosfellssveitarfjöll. The highest and east-
ernmost of these is Grímmannsfell. These mountains consist
of SE dipping Plateau Basalts, actually the Young Plateau
Basalts; morainic and other cold climate horizons occur at a
number of levels. In Grímmannsfell we find that the dipping
basalts are cut by a horizontal erosion plane at about 300 m