194 NATURAL SCIENCE. March, [893. 



situated upon the old sea-margin of the American continent, and a 

 portion of that old continental margin forms the base of its oceanic 

 deposits. I recognised the possibility of such a base for some 

 apparently oceanic islands in the passage quoted by Mr. Jukes- 

 Browne, but was not then aware that any such existed. Of course, if 

 old stratified rocks could be shown to form the base of any of the 

 mid-oceanic islands, the whole classification, and the theory which is 

 founded on it, might be imperilled ; but this has not yet been done. 



It is evident that, with island groups whose components vary in 

 size from many thousands of square miles to small sea-washed rocks,, 

 all definitions must be taken broadly and as applying to the group. 

 Even among the pre-eminently continental British Isles there are 

 many hundreds— out of the thousand of which they are said to consist — 

 which have neither mammalian, amphibian, nor reptilian inhabitants ; 

 but it will hardly be objected that such cases as these upset the 

 biological definition of continental islands. In the same manner the 

 Seychelles are classed as belonging to the Madagascar group, and 

 are, therefore, ancient continental, while Mauritius, Bourbon, and 

 Rodriguez are true oceanic islands. 



I do not know why Mr, Jukes-Browne should say that I regard 

 New Caledonia as an oceanic island. At p. 473 of Island Life I refer 

 to it as probably once connected with New Zealand ; and again, at 

 p. 485, I suppose it to have once formed an extension of New^ 

 Zealand, which, though in some respects anomalous, has all the main 

 characteristics of a continental island. 



Looking at the question broadly, as a generalisation applying to 

 all the well-marked islands and island-groups of the globe, I entirely 

 deny the validity of the conclusions expressed in the last three 

 paragraphs of Mr. Jukes-Browne's paper, conclusions which are 

 founded exclusively on islands situated upon the margin of the 

 continental area. 



Alfred R. Wallace. 



