Arkell.1956.Jurassic..

ANTARCTICA 591
Most of the islands of the southern Antilles loop are volcanic, but the
largest, South Georgia, is an exception. This consists of several thousand
metres of fine-grained sedimentaries—greywackes, shales and tuffs—
more or less acutely folded, which appear to be a continuation of the
Cretaceous flysch zone of Patagonia and Tierra del Fuego, Darwin's
'clay-slate' formation. A few ammonites have been found. One was
tentatively identified with Acanthoceras (Gregory, 1915), but later finds of
Puzosia, Tropaeum and Sanmartinoceras have proved that the upper part
at least of the sediments (Upper Cumberland Bay Series) is Aptian
(Wilckens, 1937, 1947). One of the ammonites was found in the same
beds as problematica which had previously been identified with Lower
Palaeozoic corals (Gregory, 1915). It seems that there is no palaeontological
evidence for any sediments earlier than Cretaceous in the island
(Holtedahl, 1929; Wilckens, 1932), though it is likely that the basal Cape
George Series is Palaeozoic. The Falklands, on the other hand, contain
no solid formations younger than Trias (Adie, 1952, 19526).
The only common Jurassic fossils yet known from the Antarctic regions
are plants. They have been found in Grahamland, both at the extreme
tip, at Mount Flora, Hope Bay (Halle, 1913, Adie, 1952a) and in Alexander I
Land in the extreme south-west of the peninsula (Wordie, 1948, p. 68),
where also Upper Jurassic ammonites are reported (Adie, 1952a, p. 396;
Cox, 1953, p. 3). The Jurassic ammonites so far found are said to be
Perisphinctids; an indeterminate fragment has also been figured from
James Ross Island (Spath, 1953, p. 3, pi. xii, fig. 5), but the others are
still unpublished. The famous plant-beds of Hope Bay occur in the
lower part of the mountain, in hard slaty shales that have been folded in
Tertiary times. A lacustrine origin is probable. The beds probably
represent a continuation of some part of the Jurassic plant-beds of
Patagonia, now much better known than when Halle's monograph was
published (see Feruglio, 1949, ch. viii). The Hope Bay flora comprises
at least 42 identified forms, chiefly ferns, cycadophytes and conifers. They
are not stunted, and belong to the cosmopolitan warm-temperate Jurassic
flora. The closest affinity is with the Middle Jurassic flora of Yorkshire,
with which there are nine species in common, but there are also strong
links with India and Australia.
At present Grahamland and the adjacent islands are almost completely
covered in permanent ice, and rock protrudes only here and there. The
only living flora is a meagre growth of mosses and lichens. The conclusion
is therefore inescapable that in Jurassic times Antarctica had a
much milder climate. Fossil shells and plants show that the climate was
also temperate in the Tertiary. The glacial geology, however, indicates
much more severe glaciation in the Quaternary than at present.
The small islands of Snow Hill and Seymour, close to Hope Bay, have
yielded a beautifully-preserved Upper Cretaceous (Senonian) ammonite
fauna, which likewise shows no signs of polar characteristics, but has some
species in common "with contemporary assemblages in Chile, California,
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