Rit (Vísindafélag Íslendinga) - 01.07.1962, Side 36
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basalt. This suggests that the main layer of the Young basalts
farther south and east did not exist at that ime, i.e. we are
probably concemed with the base of the Young rocks.
East of Bakkabrúnir runs a major fault line which is not
mentioned by Líndal; we find it in the gully of the Víðidalsá
below Kolugil, Fig. 18. The left part, a, consists of the nor-
mally magnetized, much infilled lavas forming the base of
the Young sediments in the north. They are here cui by 4 re-
verse and 1 normal dyke. At right, b, are lavas of reverse
magnetization, cut by normal and reverse dykes. These basalts
are fresh and contain very little infillings. A dyke, d, marks
Fig. 18. Gully of Víðidalsá near Kolugil.
Explanation in the text.
the faultline between a and b. It seems very probable that
b is younger than a. This displacement and the following
planation must be essentially older than the deposition of the
Young rocks.
The fault probably runs close to the present scarp Bákka-
brúnir, for at the southern end of the scarp, and on the east
side of Víðidalsá, we see that the floor of the sediments are
the reverse, fresh basalts, i.e. we are here on the east side of
the old displacement. Although the fault is much older than
the Young rocks it may have played a role recently, either
by small scale movement or as a zone of weakness, diverting
the Víðidalsá in the late Pleistocene into its present course.
This course, excentric in the wide valley, Fitjárdalur, and
forming a narrow gully in contrast to the normal Fitjá river,
must be very young. It seems to be the excentric and shelter-
ed position of the Young rocks, before the upper Víðidalsá
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