LITHOGENESIS OF THE BIOCLASTIC ROCKS 693 



Saxicava, etc., bore into solid rocks or into heavy shells, thus aid- 

 ing in the destruction of the mass. To a certain extent this is also 

 true of some echini. 



Earthworms are active agents in loosening and rearranging the 

 soil particles, and to a certain extent in destroying the rock masses. 

 According to Darwin, in many places over 50,000 earthworms are 

 at work in a single acre of soil. The amount of material which 

 they transport to the surface each year was estimated by Darwin to 

 be over 18 tons per acre. (4.) The lugworms or lobworms, 

 crawling through the sands along the shore, are similarly active in 



Fig. 134. Mound of white ants in the laterite region of Africa. (After 

 Branner.) 



working over the soil. They leave behind casts of sand, and the 

 amount of soil they work over has been estimated to be sometimes 

 as much as 3,147 tons per acre. (Davison-5 : ^p/.) Ants and 

 termites are also important agents in the rearrangement of the soils, 

 especially in tropical regions, where, according to Branner, they 

 "are vastly more important as geologic agents than the earthworms 

 of temperate regions." (i : 75P; 2; 3.) In Brazil the ants excavate 

 chambers and galleries, which radiate and anastomose in every di- 

 rection, and into these they carry great quantities of leaves. The 

 mounds resulting from these excavations are often from 15 to 30 

 meters long, from 3 to 6 meters across and from one-third to over 

 one meter high, and contain tons of earth. In the forests the 



