45 



ture of the sea, as is well known, as effectually barricades the- 

 free passage of many of the higher orders of marine life from 

 the shore-line of a continent or island, in which they are not 

 native, as high altitudes constitute a line of demarcation to 

 the terrestrial fauna inhabiting two separated plains of a great 

 continent. In this way it is quite possible under favourable 

 conditions that change of temperature alone may depauperate 

 marine life, or may even give an azoic appearance to deposits 

 which are of marine origin. The evidences which have led me 

 to these conclusions — that the South Australian seaboard 

 recent accumulations belong to that class of deposits — are- 

 summarily stated in the following sentences : — 



Mr. A.^Wallace states ("Distribution of Animals ;" vol. I.^ 

 page 447) : — " Between the Fiji Islands, Xew Caledonia, the- 

 tSolomon Islands, and Australia, the depth is about 1,300 

 fathoms, and between Sydney and New Zealand 2,600 fathoms, 

 showing in every case a general accordance between the depth 

 of the sea and the approximation of the several faunas." By 

 referring to a map of the world showing the undulations of the 

 ocean bed, it will be seen that the continent of Australia is sur- 

 rounded on the south and west sides b}^ a depth of water which 

 at no point is less than 15,000 feet. The sea depth between 

 New Zealand and the islands to the north as well as between 

 New Zealand and the continent of Australia, up to the 25th 

 degree of south latitude, is not less than 15,000 feet, whilst 

 the depth between New Zealand and Sydney is 600 feet more. 

 According to the facts relating to the distribution of life in 

 abyssal depths, as supplied by the Challenger reports, we might 

 infer that little or no direct intercourse can take place at 

 present between the moUuscan fauna dwelling in the shal- 

 lower waters around New Zealand, or her satellites, and 

 the south and east shores of Australia. Also, if we examine 

 the physical and pal?eontological aspects of these countries, we- 

 are led to believe that these conditions not only at present 

 exist, but that a similar state of sea depth prevailed between 

 those countries throughout a vast period of past geological 

 time. Consequently when extreme glaciation pervades the 

 southern hemisphere, a barrier is not only thus set up against 

 the direct passage of the molluscan fauna that inhabit the 

 shores of New Zealand and the islands connected therewith, 

 and the more temperate shores of southern Australia, but it 

 also prevents the free intercourse of the oceanic fauna (if there 

 be any) that inhabit the shores of Victoria and those of New 

 Zealand. 



Depending upon the consideration that no very great dif- 

 ference has arisen in the relationship of sea and land within 

 the Australian area since the period of the last great ^lacia- 



