420 APPENDIX E. 



Atlantic islands; and we can but hazard the assumption that, 

 at some very distant date, these genera existed in more eastern 

 parts of America, from whence seeds were transported across 

 the ocean. On the other hand, the transport of parent forms 

 or existing species from the continents of Europe and Africa to 

 the Atlantic islands may have been much facilitated by greater 

 extensions of land in bygone ages. Madeira, the Canaries, and 

 the Cape de Verde Islands, are all supposed to stand on a sub- 

 marine platform which skirts the coasts of Western Europe and 

 North-Western Africa, and whose submerged margin imme- 

 diately to the westward of the position of the islands descends 

 rapidly to a profound depth. The westward margin of this 

 platform was possibly the coast-line in Miocene times. An ele- 

 vation of its surface of a few hundred feet would approximate 

 the islands to the mainland very materially, and greatly facili- 

 tate transport. That they were, however, ever united to the 

 continent is opposed to the views of most competent geologists. 

 Lyell, speaking of this, says : ' The general abruptness of the 

 cliffs of all the Atlantic islands, coupled with the rapid deepening 

 of the sea outside the 100 fathom line, are characters which 

 favour the opinion that each island was formed separately by 

 igneous eruptions, and in a sea of great depth.' Moreover, the 

 Azores, whose botany in so many respects resembles that of the 

 other Atlantic islands, as distinguished from that of the con- 

 tinent, are enormously more distant from the mainland ; and 

 these islands stand on a platform of their own, separated from 

 the continental one by an ocean of profound depth ; so that 

 any theory of transport which applies to the Canarian and 

 Madeiran Archipelagos, should apply also to the Azorean. 



It remains a point of some nicety to decide whether the 

 Macaronesian islands should be regarded as a Botanical province 

 apart from the Mediterranean, or a sub-division of the latter. 

 The assemblage of American and Oriental genera which their 

 Flora contains, together with the arboreous representatives of 

 tropical Laurimce, all so entirely foreign to the European 

 Flora, would give it a title to be called a Botanical province ; 

 and to this as a further title is the prevalence of a considerable 

 proportion of North European plants, in the Northern Archi- 

 pelago especially. On the other hand, fully two-thirds of the 

 species are typical of the Mediterranean Flora, and by far the 

 majority of the remainder are derivative species of the same 



