GEOGRAPHICAL DISTRIBUTION OF ORGANIC BEINGS. 119 



Ocean, from North America to the western shores of Ire- 

 land and England ; but seeds could be transported by these 

 rare wanderers only by one means, namely, by dirt ad- 

 hering to their feet or beaks, which is in itself a rare acci- 

 dent. ETen in this case, how small would be the chance 

 of a seed falling on favorable soil and coming to maturity ! 

 But it would be a great error to argue that, because a well- 

 stocked island, like Great Britain, has not, as far as is 

 known (and it would be very difiBcult to prove this), re- 

 ceived within the last few centuries, through occasional 

 means of transport, immigrants from Europe or any 

 other continent, a poorly-stocked island, though standing 

 more remote from the mainland, would not receive col- 

 onists by similar means. Out of a hundred kinds of seeds 

 or animals transported to an island, even if far less well- 

 stocked than Britain, perhaps not more than one would 

 be so well fitted to its new home as to become natural- 

 ized. But this is no valid argument against what would 

 be effected by occasional means of transport, during the 

 long lapse of geological time, while the island was being 

 upheaved, and before it had become fully stocked with 

 inhabitants. On almost bare land, with few or no de- 

 structive insects or birds living there, nearly every seed 

 which chanced to arrive, if fitted for the climate, would 

 germinate and survive. 



DISPERSAL DURING THE GLACIAL PERIOD. 



The Glacial period is defined "as a period 

 Page 434. ^^ great cold and of enormous extension of ice 

 upon the surface of the earth. It is believed that glacial 

 periods have occurred repeatedly during the geological 

 history of the earth, but the term is generally applied to 

 the close of the Tertiary epoch, when nearly the whole of 

 Europe was subjected to an Arctic climate." 



