Acta naturalia Islandica - 01.02.1946, Blaðsíða 68

62
TRAUSTI EINARSSON
described in this paper lead to a certain conception of the formation
of the volcanic rocks in question. They definitely point to a certain
type of volcanism which only in later years has been recognized and
has hitherto not been considered in studies of Icelandic volcanism.
On account of the general acceptance at present of the view that the
Icelandic pyroclastic masses are inherently linked with sub-glacial
conditions, it has, however, been neccessary to devote much space to
a discussion of that theory in order to demonstrate its failure to
explain the observed facts. We shall now put together the main facts
which either weaken or directly contradict that theory.
There is first the interpretation of the grey conglomerates as
moraines which we have rejected on the following grounds:
1. The glacial striae of boulders embedded in the conglomerates
are at least in some cases of secondary origin.
2. Primarily striated pebbles are certainly very rare, conspicu-
ously rare for the conglomerates to be interpreted as moraines.
3. The series as a whole in which the conglomerates occur do not
suggest a glaciation.
4. The matrix of the conglomerates consists largely of glass frag-
ments, also when resting on a floor of crystalline lavas.
5. In the cases of a striated floor, it was seen that the striation
is hardly or not of glacial origin.
6. A dyke of the same material as that which makes up the con-
glomerates was found, as well as several volcanic veins of material
containing worn grains of glass and lava, and it was pointed out,
that the volcanic necks of N-Britain, the Faroes and Schwaben con-
sist of a similar chaotic, worn material as the Icelandic grey con-
glomerates, and have in some cases great resemblance to moraines.
7. The conglomerates form a part of a volcanic series, built up
without any notable interruptions of denudation, and are most natur-
ally understood as a link in the series and not as a break of it.
8. The composite series in which the conglomerates occur en-
closes lignite and petrified trees and the conglomerates are no doubt
of Tertiary age.
On the basis of these points we interpret the conglomerates as
being entirely of volcanic origin — mudflows either directly erupted
by volcanic vents or formed as a secondary product of certain erup-
tions. This conception applies to all the conglomerates mentioned