448 A TREATISE ON METAMORPHISM. 



various indefinite directions, as do the plants. The main mechanical effect 

 of the burrowing animals is to bring material from below the surface to the 

 surface. But some animals throw the soil behind them or push it up as 

 they move along. The animals which are mechanically effective upon 

 soil are (a) earthworms, (b) ants, termites, and other insects, (c) larger 

 burrowing animals, and (d) man. 



Earthworms. — As shown by Darwin, one of the most important of all the 

 animals in movements of the soil, if not the most important, is the earth- 

 worm." Earthworms are distributed throughout the world in great numbers. 

 According to Darwin there are at work in many places over 50,000 upon a 

 single acre of soil. The amount of material which the earthworms trans- 

 port to the surface of the earth in a year is very great. Darwin estimates 

 it as over 18 tons [16 tonneaus] per acre. 6 Davison states that the amount 

 of earth turned up by lobworms is sometimes 3,147 tons [2,832 tonneaus] 

 peracre. c 



Ants, termites, and other insects. — According to Brainier, of the buiTOwing work 

 of insects that of ants and termites is most important. In tropical regions 

 these " are vastly more important as geologic agents than the earth- 

 worms of temperate regions." d However, this statement should doubtless 

 be restricted to the mechanical work of turning over the soil and bringing- 

 it to the surface. In chemical work the earthworms are probably more 

 important, (See p. 456.) The ant-hills of the Tropics are of great size 

 and incredibly numerous. Branner states that the ants of Brazil live in 

 large, often enormous, colonies. They excavate in the earth chambers with 

 galleries which radiate and anastomose in every direction, and into these 

 chambers and galleries they carry great quantities of leaves. One can get 

 some idea of the extent of these openings from the heaps of earth brought 

 up by the insects. These mounds are often from 15 to 30 meters long, 

 from 3 to 6 meters across, and from one-third to over 1 meter high, and 

 contain tons of earth." 



In another place Branner states in reference to the ant-hills in the 

 forests: "These mounds are from 3 to 14 feet [1 to 4 J meters] high and 



a Darwin, Charles, The formation of vegetable mould, D. Appleton & Co., New York, 1883, 

 pp. 1-313. 



& Darwin, cit., p. 165. 



c Davison, Charles, Work done by lobworms: Geol. Mag., new ser., vol. 8, 1891, p. 491. 



d Branner, ,T. C, Ants as geological agents in the Tropics: Jour. Geol., vol. 8, 1900, p. 152. 



? Branner, J. C, Decomposition of rocks in Brazil: Bull. Geol. Soc. America, vol. 7, 1896, pp. 

 255-314. 



