Jökull - 01.12.1991, Page 61

UL : W- Úlfarsfell. The lower part is in the small but
conspicuous gully above the main road around
Hamrahlíð, ending in the tillite bed UL 14 at ca. 160
m. The upper part starts at the end of a track off road
no. 430 at about 120 m altitude.
UO : NW- Úlfarsfell. Short profile segment sampled at
the base of the cliffs, stratigraphically lower than UA.
UA: N- Úlfarsfell. Beginning at the base of the cliffs
at an elevation of about 155 m. Thin flows, difficult
to drill, so that several were omitted. Reversal from R
to N occurs at a tillite horizon above UA 18.
UB : Upper Úlfarsfell. Continuation of UA with
some overlap, beginning at about 180 m altitude. The
units numbered UB 4 and 8 could not be found dur-
ing sampling. UB 17 B,D,G are thin flows cored on a
ridge running east from the top of the mountain
(named Stórihnúkur). UB 20 is a thin vein at the peak
of Stórihnúkur and 20A is nearby pillows or blobs in
the tuff.
UC : Varmá stream. Short segment sampled, starting
above Efrihvoll where the stream leaves a steep
gully. The lower part of the segment includes some
hard irregularly jointed lavas, presumably subglacial.
UD : Hafrahlíð hill. UD 0-15 are in the brook of
Uxalækur in the Borgardalur valley, starting at about
100 m altitude. UD 0 is an isolated intrusive or lava
flow displaying irregular columnar jointing within
the tuffaceous sediment. After an unexposed gap of a
few tens of m above UD 15 the profile continues up
the peak south of Borgardalur. UD 23 are isolated
basalt pillows in tuff.
UH : Helgafell hill, from base of the compound flow
at an elevation of about 80 m to no. 14 at the top of
the hill. Sites UH 1 and 2 were close to small intru-
sives and gave very inconsistent remanence results,
so that data from these lavas have been discarded.
UH 15 is the intrusive plug Víghóll, east of Helgafell.
Two production wells of Hitaveita Reykjavíkur are in
the vicinity, about 40 m below sampling site UH 1 in
altitude. Well MG 19 (1513 m deep) is about 350 m
east of site UH 1 and well MG 37 (2000 m deep) is
about 350 m northwest of site UH 1. There is a fault
with downthrow to the west between well MG 37
and site UH 1.
REFERENCES
Einarsson, T. 1957. Magneto-geological mapping in
Iceland with the use of a compass. Adv. Phys. 6:
232-239.
Friðleifsson, I.B. 1973. Petrology and structure of the
Esja Quaternary volcanic region, SW-Iceland.
Ph.D. thesis, University of Oxford, 209 pp.
Friðleifsson, I.B. 1985. Jarðsaga Esju og nágrennis.
Arbók Ferðafélags Islands: 141-172.
Geirsdóttir, Á. 1991. Diamictites of late Pliocene age
in westem Iceland. Jökull 40 : 3-25.
Jóhannesson, H. 1985. Jarðfræði Innnesja. In: Innnes.
Náttúrufar, minjar og landnýting (ed. Kristbjörn
Egilsson). Náttúrufræðistofnun Islands og
Staðarvalsnefnd : 17-22.
Kristjánsson, L. 1984. Notes on paleomagnetic
sampling in Iceland. Jökull 34: 67-76.
Kristjánsson, L., I.B. Friðleifsson and N.D. Watkins,
1980. Stratigraphy and paleomagnetism of the
Esja, Eyrarfjall and Akrafjall mountains, SW-
Iceland. J. Geophys. 47: 31 —42.
Kristjánsson, L. and M. Sigurgeirsson 1992. The
R3-N3 and R5-N5 palaeomagnetic transition
zones in SW-Iceland revisited. J. Geomagn.
Geoel. (in press).
Sigurgeirsson, Th. 1957. Direction of magnetization
in Icelandic basalts. Adv. Phys. 6: 240-246.
Smárason, O.B., H. Tulinius, Th. Thorsteinsson, J.
Tómasson, Th. Sveinbjörnsson and V.
Hjaltadóttir 1985. Reykjavík. Hola RV-42 við
Korpuós. Borun og þrýstiprófun. National Energy
Authority Report OS-85063/JHD-28B, 62 pp.
Theodórsdóttir, S. 1972. Grímmannsfell í
Mosfellssveit. B.S. thesis, University of Iceland,
20 pp.
Thors, K. 1969. The geology of the Úlfarsfell area.
B.Sc. thesis, University of Manchester.
Thors, K. 1974. Stratigraphy of the Úlfarsfell area.
Ph.D. thesis, University of Manchester.
Torfason, H. 1974. Af Mosfellssveit. B.S. thesis,
University of Iceland.
Tómasson, J., Þ. Thorsteinsson, H. Kristmannsdóttir
and I.B. Friðleifsson 1977. Höfuðborgarsvæði.
Jarðhitarannsóknir 1965-1973. National Energy
Authority Report OSJHD 7703, 109 pp.
JÖKULL, No. 41, 1991 59