MEANS OF DISPERSAL. 1 23 



remembered that time, independently of fresh trans- 

 portals, will have tended to increase the richness of 

 insular faunas, for in the course of vast ages the de- 

 scendants of originally introduced forms will generally 

 have divided up into distinct varieties, and ultimately 

 in many cases into distinct species and genera ; indeed, 

 if such were not the case, we should almost have to 

 believe in the special creation for oceanic islands of the 

 endemic types which enter so largely into their faunas. 

 Icebergs " covered with an alluvial soil, on which 

 pine-saplings and a variety of herbaceous plants are 

 seen growing," according to Sir C. Lyell, are sometimes 

 drifted with the currents or blown along by the winds in 

 the arctic seas, and, Mr. Darwin says, they are " some- 

 times loaded with earth and stones, and have even 

 carried brushwood, bones, and the nest of a land bird," ^ 

 so that it seems just possible that terrestrial molluscs 

 or their ova may have been thus carried — though perhaps 

 very rarely — more especially during times when ice 

 extended over the now temperate regions, and the 

 safe landing of such creatures at some more or less 

 distant point, though certainly happening only with 

 extreme rarity, is perhaps not quite impossible. It has 

 been remarked, however, in a work edited by Dr. 

 R. Brown,^ that it " seems like straining a point " to 

 class ice as one of " the agents concerned in the dis- 

 persal of plants, insects, molluscs, etc." Icebergs, accord- 

 ing to this work, do not carry nearly so much debris as 



^ " Principles," ii. p. 394; " Origin," p. 328. 



' '• Our Earth and its Story " (Cassell : no date), ii. p. 310. 



