182 MR. A. B. WALLACE OK THE ZOOLOGICAL 



their sister science, and by means of the humble weeds and de- 

 spised insects inhabiting its now distant shores, can discover some 

 of those past changes which the ocean itself refuses to reveal. 

 Thej can indicate, approximately at least, where and at what 

 period former continents must have existed, from what countries 

 islands must have been separated, and at how distant an epoch the 

 rupture took place. By the invaluable indications which JNIr. 

 Darwin has deduced from the structure of coral reefs, by the 

 surveys of the ocean-bed now in progress, and by a more extensive 

 and detailed knowledge of the geographical distribution of animals 

 and plants, the naturalist may soon hope to obtain some idea of 

 the continents which have now disappeared beneath the ocean, 

 and of the general distribution of land and sea at former geological 

 epochs. 



Most writers on geographical distribution have completely over- 

 looked its connexion with well-established geological facts, and 

 have thereby created difficulties Avhere none exist. The peculiar 

 and apparently endemic faunae and florae of the oceanic islands 

 (such as the Galapagos and St. Helena) have been dwelt upon as 

 something anomalous and inexplicable. It has been imagined that 

 the more simple condition of such islands would be to have their 

 productions identical vdtli those of the nearest land, and that their 

 actual condition is an incomprehensible mystery. The very re- 

 verse of this is however the case. "We really require no specula- 

 tive hypothesis, no new theory, to explain these phenomena ; they 

 are the logical results of well-known laws of nature. The regidar 

 and vmceasing extinction of species, and their replacement by allied 

 forms, is now no hypothesis, but an established fact ; and it neces- 

 sarily produces such peculiar fauna; and florae in all but recently 

 formed or newly disrupted islands, subject of course to more or 

 less modification according to the facilities for the transmission of 

 fresh species from adjacent continents. Such phenomena therefore 

 are far from uncommon. Madagascar, Mauritius, the Moluccas, 

 New Zealand, New Caledonia, the Pacific Islands, Juan Fernan- 

 dez, the West India Islands, and many others, all present such 

 peculiarities in greater or less development. It is the instances 

 of identity of species in distant countries that presents the real 

 difficulty. AVhat was supposed to be the more normal state of 

 things is really exceptional, and requires some liypothesis for its 

 explanation. The plienomena of distribution in the Malay Archi- 

 pelago, to which I have here called attention, teach us that, how- 

 eyer narrow may be the strait separating an island from its con- 



