Acta naturalia Islandica - 01.07.1964, Síða 22

20
SIGURDUR STEINTHÓRSSON
formed laths. as opposed to the small and numerous plagioclases of the granular
rocks.
c. Distribution and description of the various rock types.
Figs. 2 and 4 show the distribution of the outcrops and rock types. The out-
crop NE of the quarry is an extension of the quarry rock, With the vesicular rock
(IV) on top of the combined granular and subophitic rock (I & II) under-
neath. The same relationships are present in the quarry, and in the outcrop S
of it. The highly porphyritic type (III) is intrusive into the main rock of the
quarry. SW and above the quarry, Rock IV is sitting on top of the quarry-group,
showing a sharp contact. At the contact the rock is light coloured and vesicular,
with definite elongation of vesicles parallel to the eontact. Upwards it becomes
finer grained, and the rock is dark and massive in the hand specimen (V).
The last 2 m or so are occupied by a vesicular slaggy rock, red in colour and
heavily weathered. It is in this rock that the black olivines are found. Thin
sections of the rock types seem to indicate that the red rock is an oxidized
derivative of the dark massive rock below.
Dark, hard, granular and sparsely porphyritic rock occupies much of the
Fig. 5. The quarry face viewed from south (Volks-
wagen for scale) and a block diagram of the quarry
showing the distribution of rock types. A: The main
rock of the quarry (I & II). B: The dark variety
of same. C: Finer grained granular. D: The vesi-
cular rock (IV). E: Inclusions and bands. The
quarry face is ca. 10 m. high.