Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 141

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Fig. 72. Miðfell, looking northeast.
U = upper reverse group; L = lower reverse group;
n = normal group. H : L = 1.
by a displacement that has lifted the underlying reverse rocks,
r2 and/or r3, still characterized by many occurrences of rhyo-
lite. As a result n2 has been wiped out in this area. The re-
verse rocks now occupy an area extending SW. Considerable
masses of primary breccia belong to these rocks, an important
case being Miðfell, Fig. 72.
Here we find two reverse groups, U probably correspond-
ing to r2, and L corresponding to r3. In between is the nor-
mal group n, i.e. n3. L consists mainly of considerably alter-
ed volcanic breccia. It is covered by a grey-brown conglo-
merate and brown sandstone. On this rests the normal lava
group, containing one layer of grey conglomerate. On the
west side of the mountain we find this succession: normal
lava group, grey morainelike conglomerate, brown sandstone-
conglomerate, two thick lavas of reverse magnetization, grey
morainelike conglomerate, reverse volcanic breccia, more or
less stratified and conformable with the normal group.
Where the floor of the morainelike conglomerate can be
seen it is noí glacially polished or striated. The conglomerates
are here most naturally understood as solifluction material
while the brown sandstones represent in part eolian material
and waterborne sand and gravel, the clay component being
largely washed out.
In Miðfell we see the block faulting to which the Plateau
was subjected and the remnant of an erosion plain at about
250 m. A reverse vertical dyke (S 32°W) cuts the dipping
layers in the west side of the mountain; it is probably young-
er than the dip.
Langholtsfjall is a further outlier of these rocks, dipping