60 



COMPANION TO TROPICAL READERS 



HOW SOILS ARE FORMED 



(See Tropical Readers, Book II, pp. 80-83.) 



Expt. 94. How Water aids in the Formation of 

 Soils. By a riverside or gully observe that 



(a) The water has worn a course for itself over the 

 land. 



(b) Many of the rocks have become broken off and 

 are still rough. 



(c) Rocks that have been rubbed against one another 

 are smooth. 



(d) Sand has been formed as a result of the breaking 

 up of rocks. 



(e) Boulders have been brought down by the river or 

 gully when in flood. 



Expt. 95. Collection of Rough and Smooth Stones. 



Collect eight stones showing various stages in the break- 

 ing up of rough rocks and the making of the smooth 

 river stone. 



Expt. 96. How Alluvial Soils are formed. 



(a) Observe that in rainy weather 

 the river is discoloured, owing to 

 clay and vegetable matter in sus- 

 pension, and that this is deposited 

 in the form of silt and mud where 

 the water flows slowly. 



(b) Collect a vessel of discoloured 

 water from a river (small children 

 should not be told to do this) or 

 drainage trench along the roadside, 

 and allow it to stand for twenty- 

 four hours (tig. 28). Pour off the water and examine 

 the residue. 



Fig. 28. Sediment in 

 River water 



