98 



FIRST YEAR SCIENCE 



as it falls is held by the moss, leaves and roots and pro- 

 tected from evaporation by the foliage, soil water will 

 continue to be supplied to the surrounding open land long 

 after it would have become dry had the forests been 

 removed. Mountain soils have been found which hold 

 back five times their own weight of water. 



A NATURAL SPRING. 

 Coming to the surface between rock layers. 



Gravity is continually pulling the soil water deeper and 

 deeper into the ground. This deep soil water is frequently 

 diverted to lower ground by impervious layers of soil or 

 rock and comes to the surface as springs, or it may come 

 gradually to the surface over a broad area a long distance 

 away from where it fell and make a region, otherwise 

 barren, fertile by subirrigating it. 



It is often very essential to stop as far as possible this 



