Acta naturalia Islandica - 01.07.1964, Síða 28

26
SIGURDUR STEINTHORSSON
contact. The light coloured rock may in that case represent an upper chilled
zone of a rock mass deeper down.
Moving upwards we encounter the main rock of the quarry. It is partly
dark in colour due to deuteric alteration, the dark variety occupying the lower
levels of the quarry face. The dark rock reappears on the top face of the block,
and in a small spot on the NE face. Overlying the main mass is the vesicular
Rock IV, which shows a definite flow structure in the field, due to the parallel
elongation of the vesicles.
A small area is occupied by a hard, non-porphyritic rock, grey in colour.
The only other place where similar rock is seen is in the Kálfshamar outcrop.
It is suggested that in both cases it is a xenolith and not an authentic member
of the rock series.
Fig. 6. Block dia-
gram showing bands
(A), “fish” (B) and
the column (C). Dark
rock to the left af-
fecting the bands and
half “fish”. Not to
scale.
In the SE corner of the quarry a number of non-porphyritic bands and
inclusions were observed. (Pl. VI b and Fig. 6). The inclusions are 15—30 cm
long, fish-like in shape, with one end rounded and the other one acute. They
all run parallel to each other, dipping ca. 30° with their blunt end towards
SW. Parallel to these inclusions, but occupying upper levels on the quarry