Acta naturalia Islandica - 01.02.1946, Page 15

ORIGIN OF THE BASIC TUFFS OF ICELAND
9
great importance, and it would therefore seem that to-day we have
arrived at a fairly true general picture of the geology of the country.
Yet, what this analysis shows is only that our present unsatisfactory
state of knowledge does not reveal any marked inconsistences in
the system. To believe, however, that the system therefore must be
correct would be to shut one’s eyes to the real state of knowledge
of Icelandic geology of to-day. I have already mentioned that the
classification of the basalts does not rest on microscopic work to
any great extent. Secondly, the interpretation of the old conglomer-
ates as moraines likewise rests entirely on their macroscopic character
Yet, the general system depends largely on the interpretation of these
conglomerates. The vast masses of basic tuffs which occupy a place
of crucial importance in the geology of the country are nearly un-
touched by petrographical methods and the dominating Basalt areas
are even macroscopically little known.
The nature of Pjeturss’ conglomerates has however in spite of the
unsatisfactory research, for a long time been considered as a settled
question. Similarly the origin of the basic tuffs (Palagonite Forma-
tion) is now believed to be pretty well understood. It is therefore
necessary to state emphatically that the present vietvs are unsatis-
factorily founded and should be thoroughly revised.
Several years ago I pointed out the need for a preliminary survey
of the country and a revision of certain important questions. In the
meantime I have worked on such a program and I believe that it is
justifiable to publish the conclusions so far arrived at.
The key to the geology of Iceland is in my opinion to be sought
in the Basic tuffs, their origin and age. Consequently they wiil be
considered first. Then I shall attempt a discrimation of the different
suites of plateau basalts and lastly the erosional features of the
plateau and their age will be considered with special reference to
the valleys and fjords of Northern Iceland.
In connexion with this work I stayed for several months in the
Geological Department of the University of Glasgow. Needless to say,
the access to the rich collection made by Dr. G. W. Tyrrell and M. A.
Peacock of Icelandic rocks was of great value to me. I am also greatly
indebted to Dr. Tyrrell for his advice and for putting his manuscript
on Icelandic basalts at my disposal. I also acknowledge my great debt
to Prof. A. E. Trueman and Dr. J. Weir, for valuable discussions and
substantial help.