SOILS AND FERTILIZERS 69 



granular particles settle at the bottom very quickly, 

 the finer granular particles, or silt, settle next, and after 

 a few hours the finest particles, or the clay, will be found 

 on top of the other deposits. 



A loam soil is a mixture of sand, clay, and silt in about 

 equal proportions. with humus, or partly decayed vege- 

 table and animal substances. We may have a clay 

 loam or a sandy loam, according as the one or the other 

 kind of particles predominates. All productive soils con- 

 tain more or less humus. 



A limy, or calcareous, soil may come from the break- 

 ing up of limestone. Like clay it is sticky when wet, 

 but crumbles easily when dry. 



As to Deposition. The action on rocks of the various 

 agencies mentioned above is called weathering. As a 

 result of slow weathering, soils are formed and some- 

 times remain in the place of formation. Such soils 

 are called sedentary. Sedentary soils may also be formed 

 by the accumulation of organic matter, peat or humus, 

 as in swamps and marshes. 



Water, ice, and wind sometimes carry soils to great 

 distances from the place of formation. Such are called 

 transported soils. 



The Amazon, the Nile, and the Mississippi, annually 

 swollen by spring rains, sweep to the seas, scattering 

 soil over their adjoining lowlands and depositing 

 large amounts at their mouths in the form of deltas. 

 Every rill and creek and river duplicates the work 

 of these large rivers in a degree proportionate to 

 its size and velocity of flow. Glaciers, those " frozen 

 streams moving slowly, but irresistibly onwards, down 

 well-defined valleys, grinding and pulverizing the 

 rock masses detached by the force and weight of 



