SOIL-FORMATION, PLANTS AND ANIMALS 



2Q 



created by other agencies, exerts sufficient pressure to force 

 them further apart and extend the fractures. Occasional 

 striking examples of the forcing apart of rock-masses 

 by plant-growth may be observed. The process is well 



Fig. 12. Growing roots of the tree have broken apart and otherwise disinte- 

 grated the granite boulder, thereby assisting in the formation of soil 



illustrated by the lifting of sidewalks and the tipping 

 over of stone fences, due to the development of trees 

 near by and even such soft tissues as those of mush- 

 rooms have been observed pushing up through cement 



