Rit (Vísindafélag Íslendinga) - 01.07.1962, Síða 113

111
meter, much rounded. The finer matrix consists of weathered
glass fragments and these are especially responsible for the
brown colour. This is a light material which has been trans-
ported from distant volcanic centres. The main mass contains
in addition coarse basalt debris, scattered fragments derived
from an older tuff layer, a few well-rounded pebbles, but else
there is not much evidence of a long transport. This material
has been transported down the slope from an originally high-
er terrain in the north. Wind and seasonal water flow may
have played considerable role, but as stratification and grad-
ing is nearly absent it may essentially have flowed as mud
streams.
In Nóngil occurs a thick altered primary breccia mass which
extends down to 100 m or lower, although it seems to belong
to the higher group. At 195 m it is covered by stratified con-
glomerate. This conglomerate horizon rises towards Stóra-
hálsfjall, where in 260 m it is covered by tuff-breccias.
In Svartagil the altered breccia mass rests at 205 m on a
10 m thick undoubted moraine which is probably m2. Below
the moraine are brown to grey fluviatile layers of fine grain,
at least 40 m thick. No lignite has been found here. Pebbles
of rhyolite occur in the lower part. The rocks in Nóngil indi-
cate a considerable vertical movement.
The brown colour of the “Palagonite Formation” has va-
rious causes. As a rule the basic glass occurring in it and
often forming a large part, is yellow-translucent in thin sec-
tion and has a brown colour when it formes fine-grained tuff,
although larger grains of it are quite black in the unweather-
ed state. Second, the glassy contituents of primary breccia
bodies are often weathered, each fragment having a coat of
yellow palagonite i.e. a watery birefringent alteration pro-
duct of the glass. Finally, we have here and in Mosfell met
with secondary brown tuff layers where it is reasonable to
assume that the weathering had a good start in course of
the transport.