42 THE DISPERSAL OF SHELLS. 



many young examples of Livincea peregra and L. stag- 

 nalis, ready to crawl away as soon as they dropped 

 from the blocks, and Playiorbis corneus and P. com- 

 plauatiis also occurred in quantity, mostly young, and 

 all living. The water had been frozen for six weeks, 

 and it is probable that most of the animals had 

 been at least a month in solid ice. A few specimens 

 of PisidiuDi pusilhnu^ also frozen up, had died.' We 

 have here a means by which the animals may almost 

 certainly cross arms of the sea, for when enclosed in 

 ice they would be effectually protected from the in- 

 jurious effects of salt water. Dr. Guppy has suggested, 

 also, that molluscs burying themselves in winter in the 

 mud at the bottoms of rivers, &c., may possibly be 

 transported, even across the sea, in the frozen mud 

 buoyed up by ice. In the shallow waters of the Lea, 

 he has noticed that after a frost of some duration, when 

 the water was frozen to the bottom, the mud beneath 

 for an inch or two was also frozen, so that on lifting up 

 a slab of the ice, a layer of frozen mud, an inch or two 

 thick, formed the lower part of the mass. But it seems 

 hardly likely that the creatures will often be landed by 

 these means on foreign shores in localities suitable for 

 the establishment of new colonies. Quite possibly, 

 however, on the breaking up of frosts, shells thus 

 enclosed in ice or frozen mud may be safely carried, 

 within their own river-basins, to great distances. 



Powerful whirlwinds, according to Sir C. Lyell, some- 



^ W. A. Gain, " Science Gossip," xxvii. (1891), 118. 



