88 Eeviews — Wallace's Island Life. 



undoubtedly popular — thej'- appeal so powerfully to tlie imagination, 

 — and may in a certain sense enhance tlie value of the volume. The 

 last chapter of Part I. discusses the earth's age, and the rate of 

 development of animals and plants. 



Part II. — When the difficulties presented by the peculiarities 

 of island, life are mastered, Mr. Wallace is of opinion that we shall 

 find it comparatively easy to deal with the less clearly defined, 

 problems of continental distribution. Hence the importance of the 

 subject. Islands have had two distinct modes of origin, and the 

 difference is fundamental. They are oceanic or continental. Darwin 

 has shown that with very few exceptions all the remoter islands of 

 the great ocean are of volcanic or of coralline formation, and that 

 none of them contained indigenous mammalia or amphibia. Con- 

 tinental islands are more varied in their geological formation, and 

 may be divided into two groups — ancient and recent. Islands of an 

 anomalous character constitute a fourth section. 



Amongst the Oceanic Islands are the Azores, Bermuda, the 

 Galapagos, St. Helena, and the Sandwich Islands. Amongst the 

 recent continental islands are the British Islands, Borneo and Java, 

 and Japan and Formosa. Madagascar is an example of the type of 

 ancient continental islands, Mdiilst Celebes and New Zealand figure 

 in the exhaustive division. 



It would clearly be impossible within the limits of a review to 

 give even a sketch of all these chapters, each of which is a little 

 treatise of itself, full of the best itiformation in that branch of 

 natural history which is connected with the geographical'distiibution 

 of animals and plants. A sample of the mode of treatment of each 

 of the three principal sections must suffice. 



1. Oceanic Islands. — The Azores, which bear the same relation to 

 Europe that the Bermudas do to America, lie in the course of the 

 south-westerly return trades, and also of the Gulf-stream. They are 

 900 miles from the coast of Port,ugal, with a maximum depth of 

 2,500 fathoms intervening, and are destitute of all terrestrial indi- 

 genous vertebrata. To the oceanic type they present a single excep- 

 tion, in that one of the islands contains a small deposit of Miocene 

 age. Thus the group may be of considerable antiquity, but tlie 

 fauna, " at all events as regards the birds, had its origin since the 

 date of the last glacial epoch." The small amount of differentiation 

 which time has effected in the birds — a bullfinch being the only 

 speciality — is one of the principal reasons for this belief in the recent 

 origin of the fauna, but the explanation to which Mr. Wallace points is 

 scarcely satisfactory. The glacial theory is a dangerous weapon even 

 in the hands of the most experienced geologists, and draws quite as 

 largely upon the unscientific imagination as Atlantis or Lemuria — 

 those especial bugbears of the author. When, therefore, he would 

 have us infer that all land birds were destroyed by the severity of 

 glaciation in a group of islands situated as these are, and at the sea- 

 level, we should at least expect him to indicate some undoubted 

 evidences of ice action in the islands themselves, before consenting to 

 entertain such a proposition. 



