The geographical distribution of animals, with a study of the relations ...

208 ZOOLOGICAL GEOGRAPHY. [part hi.tion all tends in one direction—to produce a more sombreand legs, and a more robustplumage, a greater strength of feetbill. We further find, that four of the land- birds, including theoriole, snow-bunting, and hoopoe, are not resident birds, butstraggle accidentally to the islands by stress of weather; andwe are told that every year some fresh birds are seen afterviolent storms. Add to this the fact, that the number ofspecies diminishes in the group as we go from east towest, andthat the islands are subject to fierce and frequent stormsblowing from every point of the compass,—and we have all thefacts requisite to enable us to understand how this remotearchipelago has become stocked with animal lifewithout everprobably being much nearer to Europe than it is now. Forthe islands are all volcanic, the only stratified rock that occursbeing believed to be of Miocene date.Madeira and the Canaries.—Coming next to Madeira, we findthe number of genera of land birds has increased to twenty-eight,of which seventeen are identical with those of the Azores.Someof the commonest European birds—swallows, larks, sparrows,linnets, goldfinches, ravens, and partridges, are among the additions.A gold-crested warbler, Begulus Maderensis, and a pigeon,Columba Trocaz, are peculiar to Madeira.In the Canaries we find thatthe birds have again very muchincreased, there being more than fifty genera of land birds ;butthe additions are wholly European in character, and almost allcommon European species. We find a few more peculiar species(five), while some others, including the wild canary, arecommon to all the Atlantic Islands or to the Canaries andMadeira. Here, too, the only indigenous mammalia are twoEuropean species of bats.Land SMls.-^Ihe land shellsof Madeira offer us an instructivecontrast to the birds of the Atlantic Islands. About fiftysixspecies have been found in Madeira, and forty-two in the smalladjacent islandof Porto Santo, but only twelve are common toboth, and all or almost all are distinct from their nearest alliesin Europe and North Africa. Great numbers of fossil shellsare also found in deposits of the Newer Pliocene period ; and