48 



NATURE AND PEOPBBTIES OP SOILS 



location and in tlie character of their material. The material 

 of the latter is generally sandy, more or less porous and well 

 drained. Deltas, on the other hand, are characterized by poor 



drainage and by heavy 

 soils, silt loams, clay 

 loams and clays predom- 

 inating. 



Alluvial soils, espe- 

 cially those of flood 

 plain origin, are com- 

 paratively young. Delta 

 and first bottom soils are 

 usually in need of drain- 

 age. Alluvial fans and 

 terrace soils are olten 

 loose and open to the 

 point of droughtiness. 

 The latter group is usu- 

 ally not so well sup- 

 plied with organic mat- 

 ter as are the delta and 

 flood plain soils, which 

 exist under conditions 

 where organic accumu- 

 lation is rapid. All allu- 

 vial soils are greatly in- 

 fluenced by the source 

 of the detritus. For ex- 

 ample, a red upland soil 

 will give a reddish allu- 

 vial, while a soil or rock poor in lime will certainly not be 

 parent to one rich in that constituent. Alluvial soils are gen- 

 erally richer in the essential constituents than the soils from 

 which they are a wash, as is shown by the following data 

 from North Carolina. 



Fig. 10. — The flood-plain and delta of the 

 lower Mississippi Elver. 



