Jökull - 01.12.1970, Qupperneq 78

The interglacial non tilted lava flows have
normal magnetization whereas several reversals
occur within the underlying Hreppar Series.
With regard to their position and freshness the
young lavas most reasonably belong to the
present normal polarity epoch (Brunhes) giving
a maximum age of 690,000 years (Cox 1969).
The degree of erosion of the interglacial lavas
is the only available means to estimate their
minimum age. The area was overridden by a
main glacier throughout most of the last glacia-
tion (Kjartansson 1943, 1958) which has un-
doubtedly resulted in an enormous glacial ero-
sion during this period. The present writer finds
it possible that the olivine basalts south of
Thjórsá were erupted cluring the last inter-
glacial period. On the other hand the tholeiites
are believed by the writer to date back from an
earlier interglacial period.
ACKNOWLEDGEMENTS
The ivriter is indebted to G. E. Sigvaldason
for his help in X-ray work on the zeolities, to
H. Tómasson and J. Jó?isson for useful discuss-
ions. He wishes to thank Prof. M. Schivarz-
bach and G. Pálmason for co?istructive critic-
ism of the manuscript and Peter Ward for
lingustic improvements and useful comments.
REFEREN CES
Cox, A. 1969: Geomagnetic Reversals. Science
163, 237-245.
Einarsson, Th. 1967: The extent of the Terti-
ary basalt formation and the structure of
Iceland. — In Iceland and Mid-Ocean
Ridges, Soc. Sci. Islandia „Rit“ 38, 170—
179.
Einarsson, T. 1967: The Icelandic fracture
system and the inferred causal stress field.
— In Iceland and Mid-Ocean Ridges, Soc.
Sci. Islandia „Rit“ 38, 128—141.
Fridleifsson, I. B. 1970: The Stóra Laxá Igne-
ous Complex, S. Iceland. Honours Re-
search Essay, University of St. Andrews,
Department of Geology, 1—88.
Kjartansson, G. 1943: Arnesingasaga (in Ice-
landic), p. 1—248, Reykjavík.
— 1958: (The Geology of Holt, Rangárvalla-
sýsla, South Iceland). The University Re-
76 JÖKULL 20. ÁR
search Institute, Dept. of Agriculture, Re-
ports, Series B-ll, 1—23, Reykjavík. (In Ice-
landic with an English summary).
— 1962: Geological Map of Iceland, Sheet 6
(Central South Iceland). Museum of Na-
tural History, Reykjavík.
Líndal, J. 1964: Með huga og hamri (“Mente
et malleo”, geological notes and papers),
edited by S. Thorarinsson, Reykjavík (in
Icelandic).
Mackin, J. H. 1961: A stratigraphic section in
the Yakima basalt and the Ellensburg
Formation in South-Central Washington.
State of Washington, Department of Con-
servation. Division of Mines and Geology,
Report of Investigations no. 19, 1—45.
Saemundssom K. 1967 (2): An outline of the
structure of SW-Iceland. — In Iceland and
Mid-Ocean Ridges, Soc. Sci. Islandia „Rit“
38, 151-161.
— 1967 (1): Vulkanismus und Tektonik des
Hengill-Gebietes in Siidwest-Island. Acta
Nat. Isl. 2, 7, 1-105.
Sigvaldason, G. E. 1968: Structure and products
of subaquatic volcanoes in Iceland. Contr.
Mineral. and Petrol. 18, 1—16.
Spry, A. 1962: The origin of columnar joint-
ing, particularly in basalt flows. J. Geol.
Soc. Australia 8, 191—217.
Steingrímsson, Jón. 1907: Fullkomið skrif um
Síðueld (Complete account of the Sída-
fires), edited by Th. Thoroddsen in Safn
til sögu Islands og íslenzkra bókmennta,
Vol. 4, p. 1—73. Copenhagen and Reykja-
vík.
Thorarinsso?i, S. 1960: Der Jökulsá-Canyon uncl
Asbyrgi. Petermanns Geographische Mit-
teilungen, 104, 2/3, 154—162. Gotha.
Tomkeieff, S. I. 1940: The basalts of the
Giant’s Causeway district of Northern Ice-
land. Bull. volcanol. Napoli (2), 6, 89—143.
Tómasson, H. 1962: Ytri Rangá, Geology. State
Electricity Authority, Report 8. 5. 1962 (in
Icelandic), mimeographed.
Walker, G. P. L. 1960: Zeolite zones and dike
distribution in relation to the structure of
the basalts of Eastern Iceland. J. Geology
68, 515-528.
— and I. S. E. Charmichael, 1962: Garronite,
a new zeolite from Ireland and Iceland.
Min. Mag. 33, 258, 173-186.