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prevent.  It  has  been  one  of  the  most  important  forces  and  factors 
in  the  geological  changes  which  have  so  modified  the  surface  of  the 
earth.  The  present  surface  of  the  largest  portion  of  the  United 
States  is  made  up  of  this  ‘‘sedimentary’'  or  “drift”  material  which 
has  been  moved  from  the  place  where  it  was  formed  through  the 
disintegration  and  decay  of  the  old  crystalline  rocks,  by  water,  wind, 
or  moving  ice,  and  which  has  accumulated  to  a depth  of  hundreds 
or  thousands  of  feet  over  nearly  the  entire  surface  of  the  country. 
It  is  estimated  that  the  general  surface  of  the  land  in  the  area  of  the 
crystalline  rocks  of  the  Piedmont  Plateau  has  been  lowered  at  least 
2,000  fe^t  bv  this  continual  \\  ashing.  This  vast  amount  of  material 
^ has  been  slowly  removed  and  deposited  elsewhere  by  the  very  same 
agents  which  we  are  contending  with  to-day  in  our  gullied  fields; 
for  this  denudation,  or  erosion,  is  still  going  on,  as  it  has  be(Mi  for 
ages  past. 
As  a rule  this  denudation  is  exceedingly  slow  and  the  general 
level  of  laige  tracts  of  countrv  is  not  lowered  more  than  an  inch  or 
two  in  a hundred  years.  Where  the  change  is  as  slow  as  this  it  is 
undoubtedly  of  benefit  to  the  human  race,  as  in  the  course  of  time 
it  must  carry  off  the  soil  which  have  been  used  over  and  over  again 
for  vegetation  and  expose  fresh  material  to  the  roots  of  plants. 
With  this  slow  change  the  natural  forces  are  amply  sufficient  for 
the  decav  of  the  subsoil  and  for  the  conversion  of  this  freshly  ex- 
posed material  into  a good  .-oil.  When  the  rate  of  denudation  is 
excessive,  however,  and  more  rapid  than  the  natural  decay  of  the 
.subsoil  material  which  is  exposed,  it  mav  work  serious  injury  to 
agricultural  lands. 
Along  the  banks  of  the  Ohio  River  and  iii  very  many  portions  of 
the  South  hundreds  of  fields  that  were  once  covered  with  sturdy 
forests  of  oik,  maple,  walnut,  and  pine,  and  which  bore  under  cul- 
tivation, being  cleared  of  the  natural  growth,  large  crops  of  wheat, 
maize,  tobacco  and  cotton,  mav  now  be  seen  furrowed  with  gullies 
as  with  the  wrinkles  of  age,  and  abandoned  to  brush  and  briers. 
.V  surface  layer  of  good  agricultural  soil  6 inches  deep  resulting 
from  the  slow  and  gradual  disintegration  and  decay  of  rocks  and 
accumulation  of  humus  may  have  required  hundreds  of  years  for 
its  natural  formation,  and  yet  it  is  liable  to  be  washed  away  in  a 
single  sto:  m. 
This  excessive  erosion,  or  washing,  of  lands  may  be  prevented, 
and  the  already  gullied  fields  mav  be  recovered,  and  steep  slopes 
of  loose  material  may  be  held  and  prevented  from  washing: — 
(1) .  l^y  chemical  means,  in  the  application  of  manures  and  fer- 
tilizers and  in  tln^  accumulation  of  organic  matter,  which  change 
the  texture  of  the  soil  and  make  it  more  j^orous  and  more  absorbent 
of  water,  so  that  there  is  less  to  run  off  over  the  surface. 
(2) .  P)V  means  of  cultivation  and  under-drainage,  which  prevent 
erosion  by  distributing  the  surface  flow  over  the  ground  and  in- 
crease the  amount  carried  off  hv  under-drainage. 
