THE SOIL 41 



ter (plant remains). Limestone soils, productive soils 

 covering ex^tensive areas in the southern and earstern 

 states of the United States, are examples of residual 

 soils. Frequently the limestone has completely leached 

 away, the soil consisting entirely of the impurities of the 

 original limestone and plant remains. Cumulose soils 

 are illustrated by mucks and peats which have been 

 formed under peculiar conditions, (i. e. poor drainage 

 as in swamp and bog land) alloAving the partial decay 

 and accumulation of plant remains, the growth of moss, 

 swamp grass, etc., on top exceeding the rate of decom- 

 position of the old remains, thus resulting in the de- 

 position of a soil consisting largely of organic matter. 



Transported Soils. — These are likewise formed by rock 

 distintegration, but the materials are removed from their 

 original resting places. Chief among the agencies of 

 transportation are the wind, the glaciers, and water. 



Material picked up and deposited by the wind is 

 termed loess. Loessial soils occupy a large area in the 

 prairies of the United States, and in depth they vary 

 from a few inches to perhaps 200 feet. 



The material brought down and deposited by the 

 glaciers is called glacial till or boulder clay. Soils so 

 formed are more varied in character, containing fre- 

 quently rounded stones and gravel along with much silt 

 and fine sand, the result of the grinding action of these 

 huge ice sheets, and frequently huge boulders left upon 

 the open prairies. 



,. Soils deposited through the agency of water, such as 

 the deltas of rivers, old lake bottoms, etc., are termed 

 alluvial soils, and these generally rank among our most 

 fertile soils. The delta of the Nile and the Red River 



