THE SOIL 



As the wall grows old the softer parts and the more 

 exposed parts begin to disintegrate, or wear away. The 

 wearing away is due to the 

 " weather," and therefore is 

 called " weathering." 



This " weather " which 

 can disintegrate rocks is 

 made up of three factors: 

 the moisture, the wind, 

 and changes of temper- 

 ature. The most active of 

 these factors is the mois- 

 ture. Some of the soil 

 formed by weathering 

 blows away as dust, or 

 washes away and becomes 

 mud. Some remains on 

 the walls and is the soil 

 in which we see the plants 

 growing. 



How old must walls be before 

 plants grow on them? Will this 

 happen sooner in dry or in moist 

 places ? 



Formation of Soil. All the land surface of the earth 

 came originally from beneath the sea, and was once 

 solid rock. Just as stone walls are made by the weather 

 into places where plants can grow, so the exposed part 

 of this rock is made into soil. In the disintegration of 



Tower of church at Daraga, 



Alljuy, ruined by eruption of Mayon in 

 1814, now overgrown with plants 



