xvi Life and Living Creatures 325 



rain, saving sudden floods, and by keeping up continu- 

 ous oozing in dry weather, preventing the streams from 

 dwindling away. Disintegrating action is on the whole more 

 frequent. The roots of plants and the little root-like fibres 

 of lichens serve as wedges, splitting up rocks and aiding 

 the formation of soil. Earthworms, termites, and ants 

 ( 311) aid largely in mixing and pulverising the in- 

 gredients of the soil. Boring molluscs drive long narrow 

 holes into the rocks below sea -level, and enable the 

 breakers to produce a much more rapid disintegration of 

 the cliffs than would be possible otherwise. Cray-fishes, 

 burrowing under the banks of rivers, are important agents 

 in causing changes in the direction of the stream and 

 the position of its bed. Beavers have a strange instinct 

 of felling trees and constructing dams across streams 

 to provide an expanse of water in which to build their 

 "lodges." These dams serve to accumulate a head of 

 water, and when burst by a flood the destructive force 

 of the current works great changes on surface scenery. 

 There is no living creature, large or small, which does 

 hot leave some trace of its life-work impressed upon the 

 solid globe, and although the individual result of the action 

 of most creatures may be little, the sum of the life of the 

 globe is a very potent factor in the evolution of the con- 

 ditions which ultimately determine it. 



BOOKS OF REFERENCE 

 (In addition to those mentioned in the text) 



Charles Darwin, Origin of Species, Insectivorous Plants, Forma- 

 tion of Vegetable Mould, and other books. 



A. R. Wallace, The Malay Archipelago and Island Life. 

 Macmillan and Co. 



A. Heilprin, The Distribution of Animals. International 

 Science Series. 



