Formation of Soil. 63 



from the surrounding higher land, became so heavy and so 

 thick as to rest upon the bottom of the lake, converting it 

 into a marsh of peat or humus soil. 



On the margins of larger lakes and 

 especially along the seashore, sand bars 

 or reefs are thrown up behind which 

 bodies of water are shut off and in g 

 these organic matter may accumulate b 

 in the same manner as that just de- ^ 

 scribed, giving rise to the same type of if 

 soils. 



In still other cases, on the margins 2 

 of the sea bottom, theTe flourishes a pe- | 

 culiar type of vegetation known as eel & 

 grass, which lives always beneath the 

 water at low tide in a position repre- 

 sented in Fig. 21. These grasses offer |. 

 a natural obstruction to the incoming g 

 and outgoing tidal waters, causing 

 them to throw down their sediments I 

 and thus build up the sea floor with % 

 silt containing large amounts of or- g: 

 ganic matter under conditions unfav- g 

 orable to rapid decay. As the sea floer 

 rises in this way above low tide level g* 

 the eel grass dies and another type of g- 

 swamp vegetation takes its place, as 

 between a and b in the figure, and here 

 again the formation of humus soil is 

 continued under somewhat different 

 conditions. 



75. Wind-Formed Soils. The wind 

 moving continuously over the face of 

 the land is now and long has been a potent factor in soil 

 removal and soil building. Indeed, it is probable that 

 nowhere can soils be found which do not contain many 

 wind-borne particles. Every raindrop which falls and 

 every snowflake, hovrcvcr white, brings to the field upon 



