THE INTRODUCTION OF NEW SPECIES 



have not hitherto received any, even a conjectural explana- 

 tion. The Galapagos are a volcanic group of high antiquity, 

 and have probably never been more closely connected with 

 the continent than they are at present. They must have 

 been first peopled, like other newly-formed islands, by the 

 action of winds and currents, and at a period sufficiently 

 remote to have had the original species die out, and the modi- 

 fied prototypes only remain. In the same way we can account 

 for the separate islands having each their peculiar species, 

 either on the supposition that the same original emigration 

 peopled the whole of the islands with the same species from 

 which differently modified prototypes were created, or that the 

 islands were successively peopled from each other, but that 

 new species have been created in each on the plan of the pre- 

 existing ones. St. Helena is a similar case of a very ancient 

 island having obtained an entirely peculiar, though limited, 

 flora. On the other hand, no example is known of an island 

 which can be proved geologically to be of very recent origin 

 (late in the Tertiary, for instance), and yet possesses generic 

 or family groups, or even many species peculiar to itself. 



When a range of mountains has attained a great eleva- 

 tion, and has so remained during a long geological period, 

 the species of the two sides at and near their bases will be 

 often very different, representative species of some genera 

 occurring, and even whole genera being peculiar to one side 

 only, as is remarkably seen in the case of the Andes and 

 Rocky Mountains. A similar phenomenon occurs when an 

 island has been separated from a continent at a very early 

 period. The shallow sea between the Peninsula of Malacca, 

 Java, Sumatra, and Borneo was probably a continent or large 

 island at an early epoch, and may have become submerged as 

 the volcanic ranges of Java and Sumatra were elevated ; the 

 organic results we see in the very considerable number of 

 species of animals common to some or all of these countries, 

 while at the same time a number of closely allied repre- 

 sentative species exist peculiar to each, showing that a con- 

 siderable period has elapsed since their separation. The facts 

 of geographical distribution and of geology may thus mutu- 

 ally explain each other in doubtful cases, should the prin- 

 ciples here advocated be clearly established. 



