Greinar (Vísindafélag Íslendinga) - 01.01.1976, Síða 100

98
cumstances that enabled observations on land to be combined with
work in the surrormding aquatories2
However, in the time available in three brief summer seasons it
appears impossible to solve even a small part of the problems offered
by the structure of Iceland. Therefore, all that is given below is,
firstly, based to a considerable extent on previous researches, carried
out in Iceland by different scientists during the last decades, and,
secondly, does not aspire to a complete solution of the problems
mentioned above, though, it seems, a certain clarity in them has
been achieved.
Basic data on geological structure of Iceland
The visible part of the crust of Iceland is almost entirely com-
posed of volcanic rocks. More than 90% of them are basalts, both
tholeiitic and olivine, the former dominating. Less than 10% belong
to the volcanic rocks of the intermediate and acid composition, i.e.
andesites, dacites, rhyolites, trachytes. The lavas are accompanied
by pyroclastic rocks of the same composition.
As to sedimentary rocks, they make up only a tiny part in the
section of Iceland and are represented in the basalts by lenses of
fluviatile and lacustrine deposits and tillites and on the Tjörnes
peninsula also by coastal sea sediments (2, 3, 5, 11, 12, 22, 24, 27,
31, 34, 42, 43, 47, 50, 51, and others).
The classical formula of the stratigraphy by Iceland includes four
basic divisions: a) Tertiary plateau-basalts; b) “ancient grey ba-
salts”; c) palagonite formation, known under the name of “Mo-
berg”; d) modem volcanic rocks. The first division is associated
with the Miocene age, the second with Late Pliocene — Pleisto-
cene, the third with Late Pleistocene, the fourth with Holocene. Such
division suggested a number of lapses in rock formation and first
of all a long lapse between the Tertiary plateau-basalts and the
“ancient grey basalts”, which was also confirmed by separate abso-
lute age determinations of rocks available up to present.
2. These works were conducted under the leadership of G. B. Udintsev, I. P. Kos-
minskaya, V. F. Kanaev.