Jökull - 01.12.1989, Side 74

process can be speeded up considerably by employ-
ing computerized two-dimensional image analysis.
REFERENCES
Blatt, H., G. Middleton and R. Murray. 1972. Origin
of Sedimentary Rocks. New Jersey, Prentice-Hall,
634 pp.
Clarke, G.M. and D. Cooke. 1983. A Basic Course in
Statistics. London, Edward Amold, 421 pp.
Dobkins, J.E. and R.L. Folk. 1968. Pebble Shape
Development on Tahiti-Nui. Journal of Sedimen-
tary Petrology 40, 1167-1203.
Egilson, D. 1974. Athuganir á gjallfalli í Heima-
eyjargosi 1973 (in Icelandic). Reykjavík, Univer-
sity of Iceland, BS thesis, 45 pp.
Einarsson, E. H., G. Larsen and S. Thorarinsson.
1980. The Sólheimar tephra layer and the Katla
eruption of = 1357. Acta Naturalia Islandica 28,
24 pp.
Einarsson, Th. 1965. Det submarine utbrudd ved
Vestmannaeyjar, Syd-Island (in Norwegian).
Naturen 2, 67-85.
Fisher, R.V. and H.-U. Schmincke. 1984. Pyroclastic
Rocks. Berlin, Springer-Verlag, 472 pp.
Folk, R.L. 1955. Student Operator Error in Determi-
nation of Roundness, Sphericity, and Grain Size.
Journal of Sedimentary Petrology 25, 297-301.
— 1974. Petrology of Sedimentary Rocks. Texas,
Hemphill Publishing Co., 182 pp.
Heiken, G. 1972. Morphology and petrography of
volcanic ashes. Geological Society of America
Bulletin 83, 1961-1988.
Heiken, G. and K. Wohletz. 1985. Volcanic Ash.
Berkeley, University of California Press, 246 pp.
Jóhannesson, H., R.M. Flores and J. Jónsson. 1981.
A short account of the Holocene tephrochronol-
ogy of the Snaefellsnes central volcano, Westem
Iceland. Jökull 31, 23-30.
Jónsson, J. 1978. Jarðfrœðikort af Reykjanesskaga
/-// (in Icelandic). Reykjavík, Orkustofnun OS-
JHD 7841, 303 pp.
Krumbein, W. C. 1934. Size frequency distributions
of sediments. Journal of Sedimentary Petrology 4,
65-77.
Larsen, G. and S. Thorarinsson. 1978. H4 and other
acid Hekla tephra layers. Jökull 27, 28-46.
McManus, D.A. 1963. A criticism of certain usage
of the phi notation. Journal of Sedimentary
Petrology 33, 670-674.
Norðdahl, H. 1983. Late Quaternary Stratigraphy of
Fnjóskadalur central North Iceland. Lund, Lund
University, Department of Quaternary Geology,
Thesis 12, 78 pp.
Olafsson, G. 1985. Flokkun heimilda um íslensk
gjóskulög og gjóskulagarannsóknir (in Ice-
landic). Reykjavík, University of Iceland, BS
Honours thesis, 77 pp.
Olafsson, M., P. Imsland, and Gudrún Larsen. 1984.
Nomahár II. Efni, eiginleikar og myndun (in Ice-
landic). Náttúrufrœðingurinn 53, 135-144.
Parks, J.M. 1966. Cluster analysis applied to mul-
tivariate geologic problems. Journal of Geology
74,703-715.
Self, S„ R.S.J. Sparks, B. Booth and G.P.L. Walker.
1974. The 1973 Heimaey Strombolian scoria
deposit, Iceland. Geological Magazine 111, 539-
548.
Self, S. and R.S.J. Sparks. 1978. Characteristics of
wide-spread pyroclastic deposits formed by the
interaction of silicic water and magma. Bulletin
Volcanologique 41, 196-212.
Sigurdsson, H. 1982. Utbreiðsla íslenskra gjósku-
laga á botni Atlantshafs (in Icelandic). In: Thórar-
insdóttir, H„ O.H. Oskarsson, S. Steinþórsson and
Th. Einarsson (ed.) Eldur er í norðri. Reykjavík,
Sögufélag, 119-127.
Sigurdsson, H. and R.S.J. Sparks. 1978. Rifting
episodes in north Iceland in 1874-75 and the
eruption of Askja and Sveinagjá. Bulletin Vol-
canologique 41, 1-19.
Sigvaldason, G.E. 1974. The petrology of Hekla and
origin of silicic rocks in Iceland. 'I'he Eruption of
Hekla 1947-1948. V. 1. Soc. Sci. Isl. 44 pp.
— 1979. Rifting, magmatic activity and interaction
between acid and basic liquids. The 1875 Askja
eruption in Iceland. Reykjavík, Nordic Volcanol.
Inst. Rep. 7903, 54 pp.
Sneed, E. D. and R.L. Folk. 1958. Pebbles in the
Lower Colorado River, Texas, a study in particle
morphogenesis. Journal ofGeology 66, 114-150.
72 JÖKULL, No. 39, 1989