INTRODUCTION OF FOREIGN SPECIES. I57 



siderable time immersed in water, and yet, on being 

 placed in favorable circumstances, have been found to 

 retain their vitahtj, and have matured and produced 

 young. They would not be exposed to severer trials 

 when floating upon a log in the ocean, and their chances 

 of surviving would be as good. Logs and trunks of 

 trees which have drifted from a great distance, may 

 often be seen upon our sea-beaches ; and we remember, 

 on one occasion, to have seen Nantasket beach, at the 

 mouth of Boston harbor, strewn with logs which had 

 been driven from the rivers of ]Maine by easterly winds 

 of several days continuance. 



The limits of species, and particularly of the intro- 

 duced species, are gradually enlarging, and though their 

 progress must necessarily be slow, it is susceptible of 

 satisfactory proof. Unless of native origin, as we have 

 suggested, the time of their introduction must be taken 

 to be a period subsequent to the colonization of the 

 country, which is comparatively a recent date, and yet, 

 some of them have extended over a large part of the 

 country, as Helix pulchella, and Bulimus lubriciis, and 

 are extremely abundant. The fact that the distant 

 regions to which these species seem to have extended, 

 are in the track of the early French voyagers and col- 

 onists, along the great Lakes and about the upper Mis- 

 sissippi, is quite significant ; and shows that they might 

 have been introduced into those parts directly, with the 

 effects of the colonists, in the same manner as we sup- 

 pose tliom to have been introduced on the Atlantic bor- 



