NIGER EXPEDITION. 77 
great extent, over the Atlantic Ocean, and against the pre- 
vailing direction of the winds. It may be contended that 
such a migration would have peopled these islands solely, or 
mainly, with certain of the more transportable classes of plants; 
and that the result must be, that the number of species belong- 
ing to each natural order would be great in proportion to the 
facility with which they bear transportation : while only those 
orders could be numerous, which possess that faculty in an 
eminent degree. But such are not the characteristics of the 
Mediterranean plants found in Madeira. 
On the other hand, the existence of such a continent, 
during the period when these islands bore the plants which 
they now produce, would argue the former presence of 
5 very large Flora belonging to the type which now distin- 
guishes the islands in question from the Mediterranean ; and 
of whose previous existence the remaining species, peculiar 
to them, are the indication. Against this theory it might 
be urged, that more: specific identity between the plants 
9f the several insular groups, would then be the natural 
consequence, than now is seen : for the affinity of vegetation 
between the different islands consists, not in identical species, 
but in representatives.: The same agent, in short, which 
effected the peopling of the several groups with the plants 
9f continental Europe, would also have distributed more 
equally the non-European species over the same area. - 
It is, however, to the lofty peaks of Atlas that we must 
look, if any where, for the continental representatives of 
those peculiar plants which mark the North Atlantic Insular 
Floras, Thus, we expect to find the productions of the Galapa- 
80s Archipelago on the higher levels of the Cordillera; and the 
mountains of St. Thomas, Fernando Po and the Cameroons, 
on the west coast of Tropical Africa, may yet exhibit to us the 
Botanical features of St. Helena. Outlying and high islands 
Commonly partake in the peculiar vegetation of a climate cooler 
than belongs to the low lands of the adjacent continent ; 
though, in the case of Juan Fernandez, they sometimes 
exhibit genera equally isolated in botanical affinities as their 
habitats are in geographical position. ESSE, * 
