466 ZOOLOGICAL GEOGRAPHY. [PART III. 
disappear during an entire rotation of the earth. During such 
a period, tropical forms of marine animals would have been able 
to spread north and south, into what are now cool latitudes ; and 
identical genera, and even species, might then have ranged along 
the southern shores of the old Palearctic continent, from Britain 
to the Bay of Bengal, and southward along the Malayan coasts 
to Australia. 
Numerous Miocene plant-beds have also been found in Vic- 
toria, containing abundance of Dicotyledonous leaves, which are 
said generally to resemble those of the Asiatic flora, and of the 
Miocene plant-beds of the Rhine. Itis to be hoped these beds 
will be more closely examined for remains of insects, land-shells, 
and vertebrates, and that the plants will be carefully preserved and 
critically studied; for here probably lies hidden the key, that 
will solve much of the mystery that attaches to the past history 
of the Australian fauna. 
