Revieics — Wallace's Island Life. 85 



of the distribnlion of land and water on the earth's surface ; and (3) 

 the nature and frequency of climatal changes throughout geological 

 time." 



Thus it will be perceived that this work, though dealing in the 

 main with biological questions, enters to a considerable extent into 

 ph^'sical ones, and has therefore a double claim to the notice of 

 geologists, who will be anxious to know whether the author suc- 

 ceeds in establishing the three preliminary doctrines detailed above, 

 and how far they assist him in clearing up the many anomalies of 

 Island Life. 



The first part of the book is occupied with the phenomena, laws, 

 and causes of the dispersal of organisms, wherein the author dis- 

 cusses the general features presented by animal distribution, as well 

 as the changes which have been the most important agents in 

 bringing about the present condition of the organic world. In the 

 second part he proceeds to apply the principles previously enunciated 

 in the elucidation of the phenomena appertaining to Insular Faunas 

 and Floras. 



Part I. — The first five chapters deal mainly with the zoological 

 aspects of distribution. Amongst the elementary facts some remark- 

 able instances of discontinuity even on continents are detailed, and it 

 is observed that such " numerous examples of discontinuous genera 

 and families form an important section of the facts of animal dis- 

 persal which any true theory must account' for." We may feel sure 

 that the question of Evolution as the key to Distribution is ably 

 stated by a naturalist who shares with Darwin the honour of having 

 established the most important principles as to the origin and 

 development of species and genera. The tendency to change, 

 always more or less inherent, though stimulated and taken advantage 

 of by circumstances, in combination with the powers of dispersal of 

 organisms under different conditions, may serve to explain much of 

 the existing disti'ibution of plants and anitnals. In concluding this 

 part of the subject, the author observes that the theory of Evolution 

 necessitates the former existence of a whole series of extinct genera 

 to fill up the gap between the isolated genera which in many cases 

 now alone exist, while it is almost an axiom of natural selection, 

 that such numerous forms of one type could only have been 

 developed in a wide area and under varied conditions implying a 

 great lapse of time. 



Thus far, Mr. Wallace has been on his own ground, and there are 

 few palseontologists at this time of day who are not more or less 

 convinced of the truth of the first of his three great principles or 

 doctrines. But when, in dealing with geographical and geological 

 changes, he arrives at the consideration of the second principle, 

 viz. the permanence of continents, there is by no means that 

 unanimity amongst the authorities which the statement in the 

 preface might lead the public to su^ipose. Geologists, especially in 

 England, cling to the views of the great fathers of their science, 

 and thus the opinions of Lyell and others as to a complete change 

 of land and sea having taken place over and over again are, as he 



