14 GENERAL BOTANY 



minute or two to settle. A deposit soon forms at the 

 bottom while the water becomes clearer and on it will 

 be found floating bits of leaves, roots and other 

 organic remains. Skim these off, pour the brown 

 water into a large dish and allow it to evaporate. Add 

 more water to the original deposit, stir it up, and 

 after allowing it to settle a minute or so, pour the 

 water away, and again add water to the remainder. 

 Proceeding in this way you will eventually find at the 

 bottom oT the glass hard (probably whitish) grains of 

 sand and rock, while, when the water first poured 

 off has evaporated, a layer of sticky clay will be left 

 on the dish. 



From this we learn that surface soil contains 

 (i) organic matter which floats in water, (ii) clay, and 

 (iii) sand. The reason why clay and sand separate 

 is that the former is made up of much finer par- 

 ticles, which because they are so small take longer 

 to sink, and remaining in suspension are removed in 

 the water that is poured away. You may, of course, 

 keep all the water removed at each washing. It 

 will be found that the several washings contain mix- 

 tures of clay with gradually increasing proportion of 

 sand. 



Doing the same with the subsoil, you will find that 

 there is practically no organic matter, only a few stray 

 bits of root and much less clay, but more sand and 

 bits of rock. 



So that we can trace continuous change from the 

 solid rock at the bottom to the soil at the top. 



Now the ordinary rock of South India consists of 

 a mixture of silica (which is transparent and glassy in 



