Improvement  of  Land  by  Warping.  95 
bottom,  the  process  was  seen  to  be  so  far  advanced,  that  only  another  year 
was  requisite  for  its  completion.  The  flood  in  this  instance  had  been 
much  charged  with  soil.  The  water  which  comes  off-  cultivated  land 
completes  the  process  sooner  than  that  which  comes  off  hill  and  woodland. 
Almost  the  whole  of  the  Val  di  Chiana  has  been  raised  by  the  process  of 
colmata.” 
Whoever  will  take  the  trouble  to  examine  a map  of  England, 
will  readily  perceive  that  the  peculiar  situation  of  the  counties  of 
York  and  Lincoln  with  respect  to  the  sea  offers  considerable 
advantages  for  the  prosecution  of  this  operation.  Not  only  are 
they  both  more  than  half  surrounded  by  water,  but  the  greater 
portion  also  of  the  country  so  situated  lies  considerably  below  the 
level  of  the  sea;  from  the  encroachment  of  which,  indeed,  it  is 
only  preserved  by  extensive  walls  and  embankments,  which  have 
been  erected  and  maintained  at  a great  expense.  The  water  of 
the  rivers  that  flow  through  such  a district,  as  may  be  naturally 
supposed,  is  highly  charged  with  a fine  mud,  admirably  adapted 
for  the  purposes  of  the  warper,  who  conducts  his  operations  as 
follows : An  excavation  having  been  made  in  the  river-bank, 
under  the  bed  of  the  stream,  a clough  is  built,  which  directly 
communicates  with  a main  drain  or  duct,  often  of  large  size  and 
several  feet  in  width.  This  drain  is  furnished  with  substantially- 
built  raised  embankments  of  very  solid  earth,  and  is  formed  for 
the  purpose  of  conveying  the  muddy  water  from  the  river  to  the 
land  intended  to  be  warped,  over  which  it  is  gradually  and 
equally  distributed  by  numerous  smaller  lateral  drains ; the  said 
land  having  been  previously  laid  as  nearly  upon  a level  as  cir- 
cumstances will  admit  of.  In  order  to  confine  the  water  to  this 
particular  spot,  and  prevent  it  from  overflowing  the  adjacent 
country,  the  land  is  surrounded  and  divided  into  compartments  of 
about  20  acres  in  extent  by  strong  well-formed  banks,  which  are 
of  the  same  height  as  those  of  the  main  feeder,  but  neither  so 
wide  nor  solid.  Then  again  there  is  an  inner  bank  all  round, 
which  has  openings  in  it  adjacent  to  the  lowermost  parts  of  the 
land  for  the  purpose  of  getting  the  muddy  water  to  those  places 
as  soon  as  possible.  In  this  way  each  flood-tide  is  conducted 
into  every  one  of  the  compartments  in  succession ; and,  as  it 
ebbs,  the  hydrostatic  pressure  of  the  water  alone  suffices  to  force 
open  the  swinging  doors  of  the  return  sluices,  thus  allowing  itself 
to  escape  into  the  main  canal,  and  thence  into  the  river,  after 
having  deposited  nearly  the  whole  of  its  mud  upon  the  surface  of 
the  enclosed  land.  Of  course,  the  higher  the  tides  are,  the 
greater  is  the  depth  of  water  to  produce  the  deposit,  and  vice 
versa.  Considerable  skill  is  required  to  be  exercised  in  adjusting 
the  size  of  the  doughs,  so  as  to  discharge  the  whole  of  the  water 
before  the  rise  of  the  next  tide,  as  otherwise  only  every  other  tide 
can  be  admitted. 
