Jökull - 01.12.1980, Blaðsíða 5

deposits to the Pliocene Formation and com-
pared them with the Crag Formation in Eng-
land. Paijkull (1867) described the coal beds
and marine Pliocene deposits at Tjörnes in
some detail and collected fossils. He published
a list of mollusc species that had been iden-
tified by Mörch, who later published a paper
on the molluscs of the Crag Formation of
Iceland. Mórch (1871) inferred a higher sea
temperature than at the present and pre-
sumed that the shelly deposits corresponded to
the Older Red Crag in England and Belgium.
Johnstrup (1877) visited Tjörnes and found that
the fossiliferous beds and lignites were more
extensive than previously thought. He con-
cluded that the lignites had been deposited as
coastal driftwood as they occurred along with
marine fossils. Johnstrup collected fossils from
various beds in Tjörnes and presented the
material to Mörch. In the archives of the
Geological Museum in Copenhagen there is
an unpublished manuscript dated at 1884 (cf.
Pjetursson 1905b) on the fossil Crag molluscs of
Tjörnes (Poulsen 1884). Poulsen mentioned 117
species from the Hallbjarnarstaðir deposits,
discussed the geographical distribution of
those still living, and concluded that the
deposits must be younger than the youngest
part of the English Crag Formation. Fossil
material was collected on Tjörnes by Starkie
Gardner (1885) and analyzed by Jeffreys and
Wood, who both suggested similarities between
the faunas of the Tjörnes Crag and the English
Red Crag. Jeffreys considered a younger age
possible. The first plant remains to be iden-
tified from the Tjörnes deposits were reported
by Windisch (1886), who found remnants of
trees in the Húsavík area, North Iceland.
Early ideas on the position of Tjörnes with respect to
the general geology of lceland
At the turn of the century important con-
tributions towards the knowledge of the
geology of the Tjörnes area were made by
Thoroddsen and Pjetursson. Thoroddsen (1902)
gave the first geological account of the Tjörnes
peninsula as a whole, which according to him
was built up of old basalts, late Pliocene
2H3 ■ ÍHa* EIIIi 3 E“!‘
Fig. 2. Major lithostratigraphical units on
Tjörnes. Legend: 1. Kaldakvísl lavas. 2. Tjör-
nes beds. 3. Höskuldsvík lavas. 4. Breiðavík
Group. — Mynd 2. Helstu jarðlagasyrpur á Tjör-
nesi. Skýringar: 1. Köldukvíslarhraunlóg. 2. Tjör-
neslög. 3. Höskuldsvíkurhraunlög. 4. Breiðuvíkur-
hópur.
sediments, tuffs, and breccias covered by
dolerites, and glacial sediments. Based on his
extensive studies of the geology of Iceland
during the last decades of the nineteenth cen-
tury, Thoroddsen (1906) divided the Icelandic
sequence into formations. His division is
schematically presented in Table 1 along with
later stratigraphical schemes involving Tjör-
nes.
The old basalts of Tjörnes belonged to
Thoroddsen’s Miocene Basalt Formation, which
he considered to be some 4000 m thick, the
uppermost 1000 m being separated from the
lower basalts by an extensive horizon of lig-
nites and sedimentary beds. According to
Thoroddsen a phase of tectonic disturbances
and subsidence set in towards the end of the
Miocene, followed by considerable coastal
JÖKULL 30. ÁR 3