Greinar (Vísindafélag Íslendinga) - 01.01.1977, Blaðsíða 34

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breccia masses forming the Hólsfjöll mountain chain (see be-
low). The western escarpment of the lava group itself is here
seen in Biskupsöxl, where the land drops by faulting west and
down to the lower level on which the Jökulsá á Fjöllum flows.
Biskupsöxl is the westernmost visible exposure here of our
group in the southern Hólsfjöll area, while it reappears as a
basalt plain, overlooking the Vopnafjörður dissected and lower
country. At the southwestern corner of the normally polarized
Súlendur tuffbreccia mountain, our main normal group is over-
lain by a small outcrop of reverse rock (Rln?), and in the
eastern steep side of Brunahvammsháls, the main normal group
is overlain by a thin reverse group (R2n?), which in turn is
overlain, on the top of the broad ridge, by normally polarized
tuffbreccia.
We can probably denominate the last one by (Nln), and our
main and very extensive normally polarized dolerites provis-
orily by (N3n) — as a connection between the two active zones
has so far not been carried out by stratigraphic methods in
this paper. But in Chapter 3, we shall present a new founda-
tion for comparing the activity in the various zones.
It is in the area east of the (Nln) tuffbreccia mountain chain
of Hólsfjöll, from Vatnajökull in the south and far towards
the north, that we observe a new feature of (N3n), namely a
great many N-S striking shallow valleys, eroded into the sur-
face of this dolerite group.
The valleys are rather insignificant but quite clear. They are
rather shallow, as already said, and of very low gradient to-
wards the north. These valleys have no deep gorges, such as
might have indicated erosion by glacial waters. They are simply
clear-water valleys which have developed along N-S striking
fractures, or small faults. To follow the further description,
the reader needs a map.
North running rivers on Jökuldalsheiði. Eyvindará, Víðidalur
which latter would have been a continuation of Hrafnkels-
dalur before the existence of Jökulsá, and also have continued
under the tuffbreccia volcanic mountain of Eiríksstaðahneflar,
of reverse magnetization. The inference is that the eruption