31G ANNUAL OF SCIENTIFIC DISCOVERT. 



Forbes, that in the Miocene period the European continent extended to the 

 Azores and Canaries, and supported it by fresh proofs.* In fact, the pre~ 

 dominant European character of these islands, which occurs in their insects 

 as well as in their flora, proves that they were anciently joined to the con- 

 tinent. Nevertheless, we must not forget that, as compared with Europe, 

 these islands are very different from those of the Mediterranean. They are 

 distinguished, in the first place, by a much greater number of peculiar species, 

 which constitute a third or a fifth of the plants; and in the second, by some 

 American types, which make their appearance in all these islands. There 

 are not only certain American species which might have reached them acci- 

 dentally by the agency of the winds and current*, or of man, but American 

 genera which are represented by peculiar species. I will instance the genera 

 Clcthra, Bystrobogon, and Cedronetta > as also the unique pine of the Canaries 

 (Pinus canariensis, Sm.), which belongs to the American forms with acicular 

 ternate leaves. The relaiions of the laurels is very remarkable in this re- 

 spect ; they form a great part of the forests of Madeira and the Canaries, 

 dividing into four species, and playing an important part. Two species 

 ( Oreodaplim fcetens and Persea indica) are essentially American types ; the 

 third (Plmbe jBrfo<scrna, Webb) belongs to a genus which occurs in India and 

 America; and the fourth (Laurus canariensis, Webb) corresponds with the 

 European species. By the possession of these laurel forests the islands of 

 the Atlantic differ greatly from the African continent, where they are entirely 

 wanting, and approach America rather than Africa, notwithstanding the 

 proximity of the latter. 



These facts obtain great importance by the observation that the flora of the 

 Atlantic islands has much resemblance to the Tertiary flora of Europe. 



In my " Flora Tertiaria Helvetia?," I have proved that a considerable 

 number of plants of the Tertiary epoch corresponded with species peculiar 

 to Madeira and the Canaries, in such a manner that there must be a relation 

 between the two floras. On the other hand, our Tertiary flora indicates a 

 great resemblance to the flora of the southern United States. Many per- 

 fectly characteristic genera, such as Taxodium, Sequoia, Liquidamber, Sabnl, 

 etc., were distributed over the whole of our tertiary country, and composed 

 partly of species very closely allied to those which now grow in America; 

 other genera belong equally to America and Europe (such as Quercus, Corylus, 

 Poj)ulus, Acer, etc.), and occur in the European Tertiary epoch, composed of 

 species corresponding with the American forms. We find similar cases 

 amongst the terrestrial mollusca and insects, although this is not so positive 

 as with regard to plants. 



These remarkable circumstances are explicable, if we suppose that during 

 the Tertiary epoch a terrestrial formation united the continents of Europe 

 and America, and that this surface was extended by some projection to the 

 Atlantic islands. A glance at the map of the depths of the ocean by Maury, 

 shows that the bottom of the Atlantic forms a longitudinal valley, of which 

 the deepest parts are between the twentieth and fortieth degrees of north 

 latitude, nearly at an equal distance from Europe and Africa; but that on 

 the two sides of this deep valley there is a vast maritime plateau^ which 

 includes the Atlantic islands, as well as the whole space between the Euro- 

 pean continent, Newfoundland, and Acadia. Beyond this space another long 



* DeCandolle, Geographic Botauique raisounee, p. 1310. 



