EFFECTS OF WEATHER 



travel continuously along the ground but bump along it, 

 so to speak, sometimes passing harmlessly overhead, then 

 striking the earth again and causing more havoc. Where 

 they pass over the surface of the sea the water is some- 

 times sucked in just in the same way, causing what is 

 known as a waterspout. These may do even more damage 

 than a tornado on land, for the water is sometimes carried 

 bodily on to the land, sweeping everything away in a 

 deluge. This happened many years ago in the delta of 

 the Ganges, when thousands of people perished." 



Now let us see how these winds might leave traces in 

 the geological record. When soil is exposed to the sun 

 its surface becomes dust, and the wind carries it off. 

 Even where turf protects the surface, bare places may 

 always be found whence this covering has been removed. 

 Rabbits and moles bring up the earth to the sur- 

 face ; the earthworms sometimes bring as much as ten 

 tons of earth to the surface of a single acre of turf in 

 the course of a year. The earthworms bring up only the 

 finest particles of mould ; and these, of course, are the 

 very particles readily converted into dust and borne 

 away by the wind if they are not washed away by rain. 

 In tropical countries the white ant conveys a prodigious 

 amount of fine earth up into the open air, building walls 

 sometimes sixty feet high. Although, therefore, the 

 layer of vegetable soil which covers the land appears to be 

 a permanent protection, it does not really prevent a large 

 amount of material from being removed even from grassy 

 ground. The wind carries this fine dust far and wide 

 over the land, and over the sea as well. After the erup- 



44 



