SLOWNESS OF CHANGE 185 



Animals, in burrowing, leave holes through which tree roots 

 may easily find their way when seeking water. These holes 

 also allow water to enter, so that it may dissolve the lower 

 soil material and later bring it to the surface. 



The roots of plants penetrate far into the soil, and by their 

 growth lift up large masses of ground. They even penetrate 

 minute crevices in rocks, and, as they grow, actually split 

 them apart, exposing more and more surface of the rocks to 

 the action of the other agents of weathering. 



References : 



1. 1205 : 20-21. How Humus and Subsoil are Mingled. 



2. 1304 : 40-41. Organisms as Agents of Weathering. 



3. 1601 : 18-21. Living Organisms and their Work, 

 a. 1206 : 116-117. Work of Burrowing Animals. 



6. 1207 : 317-320. The Work of Burrowing Animals. 



c. 1208 : 23-30. Organic Agents of Changes. 



d. 1302 : 59. Plant and Animal Disintegration. 



e. 1311 : 83-85. Effect of Animals on Soil. 



/. 1312 : 262. Disintegration of Rocks by Plants. 



g. 1508 : 153-154. The Usefulness of the Earthworm. 



h. 1604 : 60-89. Field Laborers. 



i. 1612 : 17-22. The Soils that Living Things have Made. 



132. SLOWNESS OF CHANGE 



When we consider the action of the various factors which 

 have changed the surface of the earth, we must not lose sight 

 of the vast, almost incalculable, period of time through which 

 they have acted. Rocks have been formed through sedimen- 

 tation, and have been pushed up by the contraction of the 

 earth's surface. They have then been worn down by rain and 

 running water, and have formed sand, which has passed to 

 the ocean, to enter once more into the formation of rock. In 



