188 Mr. A. R. Wallace on the Law which has regulated 



facilities for giving a show of probability to any such purely 

 artificial arrangements. Their death-blow was given by the 

 admirable paper of the lamented Mr. Strickland, published in 

 the ' Annals of Natural History/ in which he so clearly showed 

 the true synthetical method of discovering the Natural System. 



If we now consider the geographical distribution of animals 

 and plants upon the earth, we shall find all the facts beautifully 

 in accordance with, and readily explained by, the present hypo- 

 thesis. A country having species, genera, and whole families 

 peculiar to it, will be the necessary result of its having been 

 isolated for a long period, sufficient for many series of species to 

 have been created on the type of pre-existing ones, which, as well 

 as many of the earlier-formed species, have become extinct, and 

 thus made the groups appear isolated. If in any case the anti- 

 type had an extensive range, two or more groups of species 

 might have been formed, each varying from it in a different 

 manner, and thus producing several representative or analogous 

 groups. The Sylviada of Europe and the Sylvicolidce of North 

 America, the Heliconida of South America and the Euplceas of 

 the East, the group of Trogons inhabiting Asia, and that pecu- 

 liar to South America, are examples that may be accounted fop, 

 in this manner. I 



Such phsenomena as are exhibited by the Galapagos Islands, 

 which contain little groups of plants and animals peculiar to 

 themselves, but most nearly allied to those of South America, 

 have not hitherto received any, even a conjectural explanation. 

 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 cur- 

 rents, and at a period sufficiently remote to have had the original 

 species die out, and the modified 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 elevation, 

 and has so remained during a long geological period, the species 



