208 ZOOLOGICAL GEOGRAPHY. [part hi. 



tion all tends in one direction — to produce a more sombre 

 plumage, a greater strength of feet and legs, and a more robust 

 bill. We further find, that four of the land-birds, including the 

 oriole, snow-bunting, and hoopoe, are not resident birds, but 

 straggle accidentally to the islands by stress of weather; and 

 we are told that every year some fresh birds are seen after 

 violent storms. Add to this the fact, that the number of 

 species diminishes in the group as we go from east to west, and 

 that the islands are subject to fierce and frequent storms 

 blowing from every point of the compass, — and we have all the 

 facts requisite to enable us to understand how this remote 

 archipelago has become stocked with animal life without ever 

 probably being much nearer to Europe than it is now. For 

 the islands are all volcanic, the only stratified rock that occurs 

 bein" believed to be of Miocene date. 



Madeira and the Canaries. — Coming next to Madeira, we find 

 the number of genera of land birds has increased to twenty-eight, 

 of which seventeen are identical with those of the Azores. Some 

 of the commonest European birds — swallows, larks, sparrows, 

 linnets, goldfinches, ravens, and partridges, are among the addi- 

 tions. A gold-crested warbler, Regulus Maderensis, and a pigeon, 

 Columba Trocaz, are peculiar to Madeira. 



In the Canaries we find that the birds have again very much 

 increased, there being more than fifty genera of land birds ; but 

 the additions are wholly European in character, and almost all 

 common European species. We find a few more peculiar spe- 

 cies (five), while some others, including the wild canary, are 

 common to all the Atlantic Islands or to the Canaries and 

 Madeira. Here, too, the only indigenous mammalia are two 

 European species of bats. 



Land Shells. — The land shells of Madeira offer us an instruc- 

 tive contrast to the birds of the Atlantic Islands. About fifty- 

 six species have been found in Madeira, and forty-two in the small 

 adjacent island of Porto Santo, but only twelve are common to 

 both, and all or almost all are distinct from their nearest allies 

 in Europe and North Africa, Great numbers of fossil shells 

 are also found in deposits of the Newer Pliocene period ; and 



