94 
Improvement  of  Land  by  Warping. 
For  this  purpose,  the  river- water,  at  low  tide,  is  allowed  to  flood 
the  land  intended  to  be  so  warped  by  means  of  outlets  in  the 
banks  of  the  river,  and  prepared  channels  and  sluices,  and  it  is 
then  kept  there  until  it  has  deposited  the  mud  or  silt  with  which 
it  is  charged.  When  this  has  taken  place,  the  clear  water  is 
permitted  to  flow  off  by  other  channels  and  return  to  the  river. 
Fresh  quantities  of  water  are  then  again  admitted  at  every  suc- 
ceeding tide,  each  of  which  produces  a new  superstratum  of  sedi- 
mentary matter,  and  this  operation  is  repeated  until  the  requisite 
thickness  of  warp  has  been  obtained.  The  quantity  of  warp  so 
deposited  by  each  successive  tide  in  many  cases  exceeds  one-tenth 
of  an  inch  in  thickness ; it  varies,  however,  greatly  at  different 
periods  of  the  year,  according  as  there  is  much  or  little  fresh- 
water in  the  river  and  in  the  position  of  the  land.  By  these 
means,  then,  there  is  created  in  the  course  of  a few  months  a new 
soil  of  considerable  depth,  which  consists,  for  the  most  part,  of 
the  various  kinds  of  earth  and  undecomposed  vegetable  and 
animal  matters  which  the  waters  of  the  river  have  collected  and 
borne  along  in  their  course.  Land  so  warped  is  said  to  possess  a 
natural  power  of  production  of  the  most  remarkable  kind,  and  a 
degree  of  fertility  far  exceeding  that  which  is  produced  by  any  of 
the  ordinary  processes  of  cultivation.  In  fact,  vast  tracts  of  per- 
fectly sterile  sandy  and  peaty  soils  in  the  neighbourhood  of  the 
rivers  Humber,  Trent,  and  Ouse  are  yearly  converted  into  good 
arable  land  solely  by  the  agency  of  this  operation. 
Although  this  process  of  warping  has  been  only  known  in 
England  for  rather  more  than  one  hundred  years,  having  been 
first  practised  near  Howden,  on  the  banks  of  the  Humber,  about 
the  middle  of  the  last  century,  and  brought  prominently  before 
the  public  by  Mr.  Marshall  in  1788,  it  has  been  long  followed 
on  the  Continent,  under  a different  name,  with  great  success,  and 
is  thus  described  by  Mr.  Cadell,  in  his  ‘ Journey  in  Carniola:’ — 
“ In  the  Val  di  Chiana,  fields  that  are  too  low  are  raised  and  fertilized 
by  the  process  called  colmata,  which  is  done  in  the  following  manner 
The  field  is  surrounded  by  an  embankment  to  confine  the  water;  the  dyke 
of  the  rivulet  is  broken  down  so  as  to  admit  the  muddy  waters  of  the  high 
floods.  The  Chiana  itself  is  too  powerful  a body  of  water  for  this  purpose, 
it  is  only  the  streams  that  flow  into  the  Chiana  that  are  used.  This  water 
is  allowed  to  deposit  its  mud  upon  the  field.  The  water  is  then  let  off 
into  the  river  at  the  lower  end  of  the  field  by  a discharging  source  called 
scola,  and  in  French  canal  d’e'conlement.  The  water-course  which  con- 
ducts the  w’ater  from  a river,  either  to  a field  for  irrigation  or  a mill,  is 
called  gora.  In  this  manner  a field  will  be  raised  five  and  a half  and 
sometimes  seven  and  a half  feet  in  ten  years.  If  the  dyke  is  broken  down 
to  the  bottom,  the  field  will  be  raised  to  the  same  height  in  seven  years  : 
but  then  in  this  case  gravel  is  also  carried  in  along  with  the  mud.  In  a 
field  of  twenty-five  acres,  which  had  been  six  years  under  the  process  of 
colmata,  in  which  the  dyke  was  broken  down  to  within  three  feet  of  the 
