ROUTES OF MIGRATION 227 



the progress of that vast submergence which brought 

 the North Sea into connection with the Enghsh Channel 

 across the Strait of Dover. As previously stated, this 

 submergence undoubtedly took place in a north to south 

 direction, if the geographical distribution of birds is of 

 any value as an indication of past physical change. It 

 follows then that this area, say north of the Humber, 

 was for the most part a water area between the latter 

 locality and Denmark, before the emigration of species 

 eastwards commenced, yet not before a line of north- 

 east Emigration had progressed towards Scandinavia, as 

 is proved by the present limits of the great East to West 

 Migration that now breaks upon the east coast of 

 England in autumn. The bulk of this migration from 

 the east strikes our eastern coast-line from Yorkshire 

 southwards, just as the bulk of our northern migration 

 in spring of summer visitors is most dominant in the 

 vicinity of the Strait of Dover — eloquent proof, I take 

 it, that the North Sea plains endured longer in the 

 south than in the north. This East to West (or more 

 correctly speaking, West to East) Migration extends 

 right across England and Wales to Ireland ; and here 

 we may remark, that there is evidence to prove that the 

 Irish Sea is crossed in a direct line east to west,^ say 

 from Holyhead southwards to the north of Pembroke, 

 which is just what we ought to find if our previous view 

 of the past physical changes in the British Area is a 

 correct one. The birds that follow this east to west 



1 Here, for instance, is the report of the keeper of the Kish Bank 

 Light Vessel, stationed off Dublin Bay : " September and October 

 are the chief months for the migration of birds from the Welsh 

 coast " {Report, iv. p. 76). 



