Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 96

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dips of 20—30°. A dyke follows the contact with the verti-
cal wall of a part of (5). A layer (9a) apparently belong-
ing to (9), rests on (8).
The dyke swarm (D) seems to be younger than (7); it
marks the position of a vertical displacement of (6). The sedi-
ment (6) is here much finer than farther northwest. It does
not show the porphyritic material present in (4) and (5)
and was most likely carried by wind from a distant source.
Summarizing, we have found that after an early volcanic
phase a steep slope was formed, possibly by uplift of a cen-
tral mass. Weathering debris covered the slope with a thick
mantle. A new volcanic period produced much fragmental
material which obliterated the former slope, and an extensive
even land resulted. Over this was spread a thick layer of
weathering debris and eolian deposits; meltwater floods and
glaciers played a part in the transport of coarse material.
A further volcanic period spread lavas over the plain; these
may be assumed to belong to the wide-spread dolerite phase.
The dolerites were in turn covered with eolian sediments.
Only after this a new very steep and high slope was creat-
ed, and this was almost certainly the result of an uplift
which created the present mountain. A last volcanic phase
covered the mountain, its surface and the steep slopes, with
a mantle of bombs and bomb fragments.
Mosfell in Grímsnes.
In the south slope of Mosfell and on the lower ground
southwest of it is obtained the section shown in Fig. 48. At
the south end of the section is breccia consisting nearly ex-
clusively of bombs in a brown glassy, rather coarse matrix.
In addition there occur large blocks of finegrained basalt
lava with fluidal structure. Farther north we meet suddenly
another type of breccia, which does not contain bombs, and
very sparse brown matrix, but instead bomb fragments with
the glass crust worn off, and debrís of grey basalt. At one