20 THE AUSTRALIAN NATURALIST. 
is yet one of the rarest Queensland shells, presumably a recent 
immigrant not yet established. 
A. glance at the physical evolution of the Coral Sea and 
east coast of Queensland, may suggest a clue to the isolation 
and peculiarity of our fauna. 
According to Neumayr (Denkschr. k. Akad. d. Wiss, 
Wien., Math., Naturw. cl. L., Abth. I., Karte I-), a meri- 
dianal crease in the earth’s crust produced in Jurassic times a 
gulf, which he called the Gulf of Queensland, whose western 
shore transgressed the present east Australian coast. 
Enlarging through geological cycles this gulf grew into 
what we now know as the Tasman and the Coral Seas. 
South of the Louisiades, and east of Cape Melville, there 
occurred a sink which I venture to suggest originated in the 
Mesozoic, and increased during the whole Tertiary Period. It 
developed into the Carpenter Deep of modern geographers. 
Our knowledge of this basin is drawn from the observations 
of the ‘‘Challenger.’’ In a traverse of 1,000 miles this great 
basin preserves an unbroken depth of more than 2,000 fa- 
thoms. Temperature readings show it to be enclosed by an 
unmapped rim, whose lowest point is 1,300 fathoms. 
As the Mesozoic sink enlarged its periphery it became a 
dominant factor in land configuration. First, it broke through 
an older inner earth fold of which New Caledonia and the 
Louisiades are relics. Then continuing its work to the east- 
wards, it submerged a younger outer continental ridge on 
which the Solomons stand. Westerly it crumpled up the 
former coast of North Queensland, and, by a furthest western 
effort, broke upon Torres Strait. 
While the Coral Sea was yet a prolongation of the old 
Gulf, it offered a refuge to old forms of life. The low lati- 
tude afforded a warm unchangeable climate, and the sur- 
rounding continent secluded its inhabitants from the incursion 
and competition of other tropical fauna. When, however, 
continued subsidence to the east at last burst through the Me- 
lanesian Plateau, a flood of active competitors must have swept 
in from the open Pacific. This reached the Queensland coast 
either by creeping along the land round the Papuan Gulf or 
by direct, usually larval, transit across the Coral Sea. 
With the opening of Torres Strait, and the consequent 
outgoing current, the Queensland fauna was spread along 
North Australia to the Moluccas. By this route there es- 
caped such forms as Trigonia, Nautilus, Meleagrina maaima, 
and Megalatractus. Had such been retained east of Torres 
Strait they would have greatly heightened the peculiarity of 
the Solanderian fauna. 
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