MEANS OF DISPERSAL. I49 



mendous dust storms, or " darling showers," which 

 sometimes blow over the country, carrying with them 

 twigs, leaves, dust, etc. ; at times also, he says, more 

 frequently in dry seasons than in wet ones, dust-columns 

 are formed, which, travelling with a rotary motion, 

 whirl up to a height light articles of all kinds that may 

 happen to be within their reach. Mr. Belt, when in 

 Australia, saw scores of these dust-whirlwinds, many 

 rising to a height of over a hundred feet, and some 

 strong enough to tear off limbs of trees, and carry up 

 the tents of gold-diggers into the air. Many were 

 observed on a small plain near Maryborough, in Vic- 

 toria, where in calm sultry weather during the heat of 

 the day, two or more were often in action at once on 

 different parts of the plain ; the dust and leaves carried 

 up rendered their spiral movement very conspicuous, 

 as, lasting several minutes, they slowly moved across 

 the plain like great pillars of smoke. From whirlwinds 

 of this sort, Mr. Belt remarks, there is a complete grada- 

 tion through larger whirlwinds and tornadoes to the 

 awful typhoons and cyclones of China and the West 

 Indies.^ As helping us to understand what may be 

 done by causes of the present kind, short accounts of 

 two rather powerful whirlwinds, one of which occurred 

 in our own islands, may be given. Sir C. Lyell 

 writes : 



*' Dr. Franklin tells us, in one of his letters, that he 

 saw, in Maryland, a whirlwind which began by taking 



^ Thomas Belt, "Naturalist in Nicaragua," ed. 2, (1888), pp. 

 301-4. 



