Rit (Vísindafélag Íslendinga) - 01.07.1962, Síða 75

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to 560 m at Súlnakvísl and falls finally to 460 m near Króka-
tjarnir. Except in a few gullies the contact is, however, hid-
den and the nature of the contact surface cannot he seen;
the abrupt changes in elevation are probably due to faults.
Near Krókatjarnir is found the section shown in Fig. 33.
On the Plateau Basalts (1) rests a formation, at least 200 m
thick, consisting of horizontally stratified tuffbreccia. The
mass is a considerably altered and cemented succession of
many layers of primary tuff, brown breccia of small blocks,
and various grades in between. Against a steep erosional
slope, cutting this mass, leans the remnant of a much younger
volcanic mass, consisting of irregularly columnar basalt. This
observation demonstrates the existence of two widely separat-
ed volcanic phases in the Súlur massif.
The main structure will now be studied in the steep east-
ern wall. All the primary volcanic rocks here found are of
normal polarity.
The stratified tuff-breccia just mentioned extends right to
the centre of the massif, Fig. 34, and has a very slight NE dip.
There is a number of concordant basalt sills, among them one
which consists of pillow lava. From one of the pillows an apo-
physis protrudes up into the roof of the sill, showing that the
pillow lava is intrusive.
This tuff-breccia formation reaches a height of about 950 m
in the easternmost peak of the massif and is here cut by a
number of thin dykes. On both sides of this peak are found
remnants of a succession of horizontal lavas with a maxi-
mum thickness of 100 m. A dyke cuts the lava series. This
lava series rests on a stratified layer of gravel, sand, and la-
minated clay with a thickness of 2m and more. The gravel
is considerably worn, probably worked by wind but not of
fluviatile origin.
This sediment and the lava series is a proof that the topo-
graphy has changed very much since they were deposited.
The stratified tuff-breccia must be considered as a remnant
of a very extensive thick layer, formed before the deep valley