n. III. OR POISONED BY VEGETABLE GROWTH? 145 



of depth, saltness, freshness, or temperature of the 

 water, separate aquatic districts. M. Alph. De CandoUe, 

 son of the great De CandoUe, enumerates twenty-seven 

 great nations of distinct indigenous aboriginal plants. 

 That the plants and animals of such vast districts of 

 stations as America and Australia should be different 

 from those of every other part of the globe, from which 

 they are so completely divided, does not strike one 

 with so much astonishment as that there should be 

 ' found one assemblage of species in China, another in 

 the countries bordering the Black Sea, and a third in 

 those surrounding the Mediterranean.' Here distance 

 and prior occupancy seem to take the duties of natural 

 barriers. But however small, and however compara- 

 tively modern the spot, if it be inclosed by natural bar- 

 riers (as, for instance, St. Helena) it will apparently 

 have a creation for itself. 



So in the Galapagos islands, of which there are ten 

 principal islands, under the line, 600 miles westward of 

 America, of modern origin, judging from the fresh ap- 

 pearance of about 2,000 craters, Lyell says of them : 

 ' Although each small island is not more than fifty or 

 sixty miles apart, and most of them are in sight of each 

 other, formed of precisely the same rock, rising nearly 

 to an equal height, and placed under a similar climate, 

 they are tenanted each by a different set of beings.' 

 ' Of twenty-six different species of land birds found in 

 the Galapagos archipelago, all, with the exception of 

 one, are distinct from those inhabiting other parts of the 



L 



