of Danah Archlppus. 97 



the agency of the winds in seizing them during the |)eriod 

 of their migration (the autumnal especially), when they 

 follow the coast, or cross its curves. Carried off, away 

 out to sea, mainly from about the lat. of 45° (the line of 

 greatest intensity of the winds), the first land they can 

 make is that of England, whence the fact, that most of 

 the species have occurred in the British Islands.* 



Winds alone can scarcely be considered the only cause 

 of the migration of butterflies over wide areas of sea, 

 though of the highest efficacy for the pm-pose. When 

 met with far away from land they seem glad to alight 

 on the vessel for rest, and no doubt vast numbers must 

 succumb to the waves ; for, apart from the vigour required 

 to sustain such a long flight, the spray in rough weather 

 would sufficiently damp their wings to prevent any onward 

 progress, and very rarely would one be likely to survive 

 the long flight across the breadth of the ocean. That the 

 flight of butterflies is often powerful is sufficiently well 

 known; and Mr. Home states he has seen them "keep 

 up with an Indian railway train, going at the rate of about 

 twenty-eight miles an hour, with the greatest ease for a 

 considerable time."t 



There is still another means of transit between the 

 Xearctic home of D. Ai-chippus and these shores. The 

 Gulf Stream, that " river of the ocean," is ever flowing 

 towards us, bearing its flotsam and jetsam of trees, roots 

 and other natural debris. On the northern coast of Spitz- 

 bergen has been found " entada gigalobium," a bean of 

 tropical America, discovered also on all the shores washed 

 by the Gulf Stream from Florida to Norway. | The drift 

 wood from the West Indian Islands is found in consider- 

 able quantity on the south coast of Iceland, where, " on 

 the beach under Snaefell, trees with their roots and scrajjs 

 of bark, logs of mahogany, and seeds which grow in 

 Jamaica at the nearest, roll in the surf."§ Sir Charles 

 Lyell quotes the instance of a boa constrictor conveyed 

 alive by the current to the island of St. Vincent, twisted 

 round the trunk of a large sound cedar tree. || IJut even 

 to our own shores have arrived at various times the same 



* Am. Journ. of Science and Arts, Jan. 18C5; reprint in Ibis, 18G7, 

 p. 2.->7, &c. 



f Zoiilugist, New Ser. p. 17(;7. 



j Kipley's and Dana's Am. Cyclnpaedin, -vol. ii. p. 77. 



§ Fn'St/and Fire, vol, i. ]>. 4M. 



jl Tiin. Geology, vol. ii. p. '.WJ. 



