16 GENERAL BOTANY 



the land by the rapid currents further up stream, 

 where the water flows less quickly, the heavier sand 

 particles in it are dropped to the bottom, while the 

 finer clay and the lighter organic matter are swept 

 further on. For the same reason that the clay is 

 swept away the seashore is, if there are no rocks, 

 always sandy. But towards its mouth where a river 

 meets the sea, its current being checked still more, most 

 of the clay is dropped too, so that the action of our 

 rivers is to remove soil from the up-country and hilly 

 tracts, to leave the sand on the plains when they begin 

 to flow slowly, and the finer particles of clay and 

 organic matter near the coast, or wherever the current 

 is checked (e.g. in irrigation works). 



Soils differ very much in their physical characters. 

 Every one knows that water easily runs through sand 

 but is retained by clay a sandy soil is soon dry 

 after rain, while on a clayey soil the water stands in 

 shallow pools. But there is also a considerable differ- 

 ence in the amount of water each will hold. To see 

 this take samples of clay or clayey soil (such as the 

 clay used for bricks and pots or black cotton soil), 

 ordinary garden soil and sand, well dry them in the 

 sun or in an oven, and fill a small vessel say an 

 ollock measure with each, weigh these, then put them 

 severally into large funnels, fitted with a thick filter 

 of blotting paper or a plug of cotton wool to keep the 

 soil from running through, and pour water on till each 

 is thoroughly wet, allow the superfluous w r ater to drain 

 away underneath, and emptying out the wet samples 

 weigh them. You will be surprised to find the enor- 

 mous difference between the retentiveness of different 



