PRESIDENTIAL ADDRESS. 



27 



that they may be read as a self-registering thermometer 

 (fig. 2) telling that when and where they lived, a climate 

 like that of, let us say, Bundaberg prevailed. At such a 

 time crocodiles may have swum up 

 the Hunter River, a Rhizophora 

 forest would have flourished on its 

 banks, and turtles may have come 

 to the predecessor of Stockton 

 beach to lay their eggs. 



Fig. 1. Arcularia 

 dorsata a member of 

 the Maitland beach 

 fauna. 



While the fauna of the deep sea 

 is probably the most conservative 

 in the world, that of the beach 

 zone appears to be less stable than 

 the ordinary land fauna. The least 

 fluctuation of temperature evokes g^ re re ^ ired by A ' 

 a response from northern species 



pressing south and southern species moving north. Here 

 are two armies perpetually in advance or retreat. 

 Tropical forms such as Bonellia 1 incessantly attempt to 

 colonise our coast, when the Notonectian floods the port, 



Fig. 2. Recession north- 

 wards in recent geological 

 time of the minimum tem- 



1 Hedley, Proc. Linn. Soc. N.S. Wales, xxxi, 1906, p. 462. 



