Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 69

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mantle has a thickness of 30—40 m, and it is covered by the
remnant of a lava. The stratification of the tuff is here rather
irregular, and the coarseness is variable; the tuff may large-
ly have been blown to this place from the slopes rather than
settled directly from the air. The tuff has here filled the ori-
ginal river channel, mentioned before, and is in contact with
the striated vertical wall of the channel. The tuff rests on
fluviatile conglomerate, which overlies a V2 m layer of brown
mudstone that rests on the striated basalt floor of the channel.
The Botnsá has cut a gully through the tuff and on the
floor of that gully is a hard moraine containing fragments
from Hvalfell material. Thus the gully is older than post-
glacial.
The tuff is here cut by basalt veins and larger intrusive
masses. The extrusion of lavas was not restricted to the cen-
tral crater. In the floor of the valley as far west as the farm
Botn and in the valley slope at Svartihryggur material was
poured out after the tuff phase, producing mainly a coarse
breccia.1)
Fig. 29. Contact of the Hvalfell rocks with the slope (s—s) of the old
Botn valley. G = Edge of Glymur waterfall; further explanation in
the text.
In Fig. 29 is shown the contact of the young rocks with the
slope of the old valley. K is a breccia, probably mainly re-
hardened scree from Hvalfell, as well as moraines; f, g and i
belong to the hasalt plateau. (The letters used are the same
as in Fig. 5 in Einarsson 1946, which was reproduced from
Pjeturss 1904). On the lava f is the erosional remnant of an-
other lava and beside it the conglomerate g.
2) Svartihryggur is a primary volcanic hreccia, as verified by its mag-
netization; it is not “recemented scree” as assumed by Rutten (1958).