426 



INSULAR FLORAS AND FAUNAS WITH 



[Ch. XLI. 



Styx by 72 feet^ may perhaps mark the site of isolated 

 volcanic cones whicli once rose above the sea-level. But that 

 the whole space within the 100 fathom line^ was ever con- 

 tinnons land, I can by no means conceive. Such an ex- 



tension would give to Porto Santo 

 dimensions. The proportion of exti: 

 to the living ones in Madeira and 



times 



present 



com 



may perhaps be slightly diminished 



some 



modern 



disappear, for it is even greater than is expressed by the 

 numerical statements above given, some species formerly 

 most dominant being now very feebly represented, and some 

 fossil races as well as species having become extinct. 



The landshells of the Canaries, when we exclude those 

 which have probably been introduced by man, are very 

 Hisfiurt from those of Madeira. The different islands in the 



more snecies m common 



Madeiras 



remote 



known period at which the aboriginal inhabitants, the 



_ » 



Guanchos, settled tliere. 



Contrast of the testaceous fauna of the British isles and that 

 of the Atlantic islands. — I shall now revert to the extraordinary 

 contrast between the distribution of landshells in the At- 

 lantic and British islands. If a curved line be drawn from 

 the Azores through Madeira to the Canaries, its length would 

 be about 750 miles, or about equal to a line drawn from the 

 Shetland islands through Scotland and England to the Scilly 

 islands. The British archipelago contains more than 200 



...^._., „..^.. ,.^...^.^..^ ..... ^._..^„ds, Orkneys, Hebrides, and 

 others. In all of these the landshells are the same, whereas 

 in the Atlantic archipelagos it is not only the principal or 

 habitable islands, but almost every uninhabited rock ofP the 

 coast, which supplies the conchologist with peculiar species 

 or varieties. In the British area, it would seem at first sight, 

 as if the land-snails had never had any difficulty in crossing 

 the sea, whereas in the Atlantic archipelagos the narrowest 



* See Map, %. 137, p. 405. 



