XXXYl 



anomalous forms, representative, it is considered, of types ages ago 

 extinct on continents. Such islands, however, differ greatly from 

 each other as to degree of peculiarity in their productions, and it 

 often happens that species identical, or nearly so, with those found 

 in the nearest continent, form nearly the whole of their present 

 inhabitants. Thus the investigation of the origin of their faunas 

 and floras is necessarily exceedingly complex. Geology has to be 

 invoked to ascertain whether the islands are of recent or ancient 

 elevation above the sea-surface, and whether the supposition is ad- 

 missible of a recent connection with the nearest continental land. 

 Oceanic hydrography and deep-sea soundings have to be studied 

 in reference to the depth of the surrounding seas, the force and 

 direction of currents and winds ; for these must all be taken into 

 consideration in discussions on the probable derivation of the 

 curious mixture of forms which is often found on these isolated 

 spots. On the other hand, it must be noted that the fauna and 

 flora themselves throw light on the geographical and geological 

 relations of the islands to the nearest land. In fact, the classifi- 

 cation of islands into oceanic and continental is founded quite as 

 much on resemblance or difference in organic productions, between 

 islands and the mainland, as on relative proximity. Thus Great 

 Britain is classed as a continental island, quite as much because its 

 fauna and flora are nearly identical with those of continental Europe 

 as because it is separated only by a shallow sea, and is now known 

 to have been actually connected in recent geological times. In 

 these investigations Entomology is now generally admitted to have 

 great importance, owing to the large number and variety of species 

 which it offers, as elements in the elaborate comparisons which have 

 to be instituted. At present authors hold the widest differences of 

 opinion regarding the subject of oceanic islands; whilst Mr. Wol- 

 laston and Mr. Andrew Murray, following the example of Edward 

 Forbes, maintain that the islands must, at a period geologically 

 recent, have been connected b}^ land with the continents from 

 which they appear to have derived the greater portion of their 

 species. Sir Charles Lyell maintains that geological facts and 

 considerations quite forbid this conclusion. It is probable that 

 the learned Entomologists just named much underrate the amount 

 of migration and dissemination, by winds and currents and other 

 means, which is slowly going on, and which is sufficient, in the 

 course of the countless centuries during which the geogi'aphical 



