THE GLACIAL RANGE CONTRACTION, ETC. 105 



fact in the comparative poorness of the avifauna of 

 Ireland and England, especially as regards southern 

 types ; or even, yet again, the poorness of the south- 

 west of England, in summer migrants especially, as 

 compared with the eastern counties — a subject which 

 also will be referred to in greater detail in a later 

 chapter. I should say in every case the probability is 

 that the abnormal migrants to our area of the species 

 tabulated above are from the East. They belong to 

 species of an eastern origin, which to reach our islands 

 normally would either have to increase or extend their 

 range southwards — contrary to Law — or to have crossed 

 wide expanses of sea, which all our experience of 

 migration and of the laws which govern the dispersal 

 of birds over the earth's surface tend to show they are 

 most averse to do. 



In an earlier chapter I alluded to a greater extension 

 of land area between Greenland and Europe during 

 Post-Glacial time ; it now becomes necessary, in order 

 to render this portion of our subject tolerably complete, 

 to enter more fully into this question and to inquire 

 whether during post-glacial time any Palaearctic species 

 has had a purely Nearctic origin. As may naturally be 

 inferred by a reference to the map, Greenland — the great 

 central land mass between Europe and America — is much 

 too isolated from what is now continental land and too 

 ice-clad to possess a very extensive avifauna. Avian 

 Emigration to Greenland appears to have been as 

 difficult from America as from Europe, even more so, the 

 wide, deep water areas (600 miles across) of the south 

 proving so effectual a barrier to extension of area in this 

 direction that not a single purely American land bird 



