Rit (Vísindafélag Íslendinga) - 01.07.1962, Blaðsíða 92

90
a) Mosaskarðsfjall-Fagradalsfjall—Brekknafjöll,
b) Jarlhettur,
c) An unnamed row 1 km east of Jarlhettur.
A section of the first, dug by a former outlet of lake Haga-
vatn, is shown in Fig. 46. The Jarlhettur cones are largelý
hidden in a Scree cover but they seem to consist of kubba-
berg. It is possible that these 3 rows were formed by sub-
glacial eruptions although by the bad outcrops this is not
more than a hypothesis, which mainly is suggested hy the
forms.
Bláfell. It is convenient to include Bláfell in the present
cluster although that means straining unnaturally the name
of this section.
The section shown in Fig47 was studied in the north wall
of the valley opposite Geldingafell.
This wall consists of primary volcanic material (áll of nor-
mal magnetization) as well as scree, eolian deposits, and coar-
ser weathering debris. The former, which are either porphyri-
tic or unporphyritic, have come from a volcanid centre near
the present centre of the mountain. Here originates a dyke
swarm (D), here is a large mass of volcanic breccia (B), and
intense alterations. The lavas (L) of nearly unporphyritic
basalt belong to the older part of the structure. We are here
mainly concerned with the younger parts.
(1) is a fine-grained stratified breccia consisting in part of
porphyritic basalt fragments on which glass coating is com-
mon, and in part of fragments of a different, nearly unpor-
phyritic basált, devoid of glass coating. The former is a pri-
iriary volcanic product, as evidenced hy larger magnetized
lumps; the latter may form separate layers with fragments
of up to 50 cm in diameter and is probably scree derived
from older material, rather than material torn from the vol-
canic funnel.
These layers were cut by a steep slope facing NW, on which
dipping layers were deposited. (2) is a breccia very largely
of the porphyritic material, the glass coating being only partly