NATURE AND FORMATION OF SOILS. ]5 



Experiment 2. — (a) Weigh a glass fruit jar, and col- 

 lect in it the clouded or muddy water — from a gullj- or 

 stream, after a rain — and allow it to stand until clear. 



(d) Weigh again; then carefully pour off the water, 

 and weigh the sediment remaining in the jar. 



(c) Calculate the per cent, of sediment. 



(i) Rivers. — When rivers overflow their 

 banks the water loses its velocity, and a layer 

 of sediment is deposited on either side of the 

 stream. In the great rivers these flood-plains 

 are broad fertile tracts of land very valuable for 

 agriculture. Those of the Mississippi are many 

 miles in width, but have to be protected by 

 levees from the overflowing of the river. 



Where the river empties into the quiet waters 

 of a lake or sea the velocity is checked and the 

 stream deposits its load. As the stream slack- 

 ens the heavier particles are dropped first, and 

 so on, until in the quiet waters only the finest 

 silt is carried. Hence it is that, on lake or sea- 

 shore, we find the coarser materials thrown down 

 first, and farther out the finer sands (Fig. 4). 

 There is usually a pause after such deposition 

 is made until a fresh supply of sediment is ob- 

 tained. This allows the surface to assume a 

 somewhat different arrangement. This surface 

 forms the plane of contact for the next layer, 

 and is called the "stratification plane." 



Experiment 3. — The assorting power of water may be 

 illustrated by (a) placing a mixture of rock material of 



