The evidence in favour of a former land-connection between Scandinavia and Greenland, rests on many other facts besides those already brought forward. That some form of land-connection formerly existed between Europe and Greenland is now indeed almost universally accepted. That it was situated more to the south between Scotland and Greenland is a supposition which has been actively supported by many leading authorities, but it seems to me that if such a land-bridge existed, it must have been in very early Tertiary times, whilst the northern one, such as I have indicated, may have originated later and persisted until a recent geological date.
The distribution of few groups of animals is now better known than that of the larger butterflies and moths (_Macro-lepidoptera_); even those of Siberia have been fairly well investigated. The interesting facts obtainable from their distribution are therefore of special value. No less than 243 species of _Lepidoptera_ are mentioned by Möschler as being common to North America and Europe. It is extremely probable that a fair number of these have either migrated direct from America to Europe or _vice versâ_, though many may be of Asiatic origin, and have wandered east and west from their original home. The following twelve species are mentioned by Petersen (p. 38) as occurring in Arctic Europe and also in Arctic North America, but not in Asia:--_Colias nastes_, _Colias hecla_, _Syrichthus centaureæ_, _Pachnobia carnea_, _Plusia parilis_, _Anarta Richardsoni_, _Anarta Schönherri_, _Anarta lapponica_, _Anarta Zetterstedti_, _Cidaria frigidaria_, _Cidaria polata_, _Eupithecia hyperboreata_; and these, as he remarks, point to the possibility of a former direct land-connection between Europe and North America.
Mr. Petersen believes that the chief immigration into the Arctic area of Europe is post-glacial and took place from Siberia, since the majority of the species are still to be found in that country at the present day (p. 57). He also draws particular attention to a fact,--which I shall discuss more fully in the next chapter,--namely, that the most characteristically Arctic forms of Northern Europe, which also partly occur in the Alps, are entirely absent from the Caucasus.