AIE.  HORNEE  ON  THE  ALLUVIAL  LAND  OF  EGYPT.  71 
feet. 
In  Pit  No.  3,  475  yards  east  of  No.  2,  on  24th  July  1852  . . . 13-0 
In  Pit  No.  4,  246  yards  east  of  No.  3,  on  24th  July  1852  . . . 19‘3 
In  Pit  No.  5,  517  yards  east  of  No.  4,  on  24th  July  1852  . . . 13‘3 
In  Pit  No.  6,  333  yards  east  of  No.  5,  on  25th  July  1852  . . . 14-9 
In  Pit  No.  7,  150  yards  east  of  No.  6,  on  25th  July  1852  . . . 17’3 
In  Pit  No.  8,  354  yards  east  of  No.  7,  on  25th  July  1852  . . . 16’6 
On  all  occasions  when  the  soil  was  penetrated,  the  progress  of  excavation  was  stopped, 
except  in  the  second  shaft  at  the  colossal  statue,  by  filtration  water,  after  which 
the  further  examination  could  only  be  made  by  borings.  This  impediment  I did 
not  anticipate ; and  I fear  that  it  must  ever  be  found  a great  obstacle  to  any  satisfactory 
ascertaining  of  the  nature  and  depth  of  the  entire  amount  of  Nile  sediment  in  any  sec- 
tion of  the  valley.  It  is  a well-authenticated  fact,  that  no  wells  can  be  sunk  with  any 
certainty  as  to  the  depth  at  which  water  will  be  found,  in  any  part  of  the  valley,  even 
within  a comparatively  limited  space.  This  irregularity  in  the  levels  must  be  caused  to 
a great  extent  by  differences  in  the  degrees  of  permeability  and  power  of  retention  in 
the  soils ; but  it  will  be  seen,  on  examining  the  sections  in  the  instances  quoted  above, 
that  the  soils  of  the  different  pits  are  very  much  of  the  same  kind,  and  it  is  not  very 
likely  that  there  would  be  great  changes  in  the  intervening  spaces. 
THE  RATE  OF  SECULAR  INCREASE  OF  THE  ALLUVIAL  LAND. 
I shall  now  proceed  to  consider  the  geological  conclusions  which  appear  to  me  to  be 
fairly  deducible  from  the  facts  which  these  researches  have  disclosed,  with  reference  to 
the  object  for  which  they  were  undertaken,  viz.  to  endeavour,  by  digging  deep  into  the 
soil  at  appropriate  places,  to  ascertain  how  nearly  we  can  determine  the  rate  of  secular 
increase  of  the  alluvial  land  by  the  sediment  left  upon  it  annually  by  the  inundation, 
and  thence  to  form  a probable  estimate  of  the  time  that  has  elapsed  since  the  lowest 
part  of  the  sediment  to  which  we  could  reach  was  deposited.  But  before  entering  upon 
this  part  of  my  memoir,  it  is  necessary  that  I should  draw  attention  to  the  inquiries  of 
a similar  natm’e  which  were  instituted  by  the  French  Engineers  who  accompanied  the 
expedition  under  General  Boxapaete  at  the  close  of  the  last  century,  as  recorded  in  the 
celebrated  work,  the  ‘ Desceiptiox  de  l’Egypte.’ 
In  books  that  have  appeared  since  the  publication  of  that  great  work  in  1809,  when 
the  formation  of  the  alluvial  land  of  Egypt  is  referred  to,  it  is  generally  assumed  as  a 
settled  point,  that  the  mean  increase  of  that  land  has  been  at  the  rate  of  5 inches  in  a 
century,  all  over  the  valley  from  Assouan  to  Cau’o*.  The  authority  relied  upon  is  the 
* Thus,  for  example,  AI.  Elie  de  Beaumont,  in  his  ‘ Le9ons  de  Geologie  Pratique,’  published  in  1845, 
p.  480,  says, — “ dans  la  Vallee  d’Egypte,  I’exhaussement  du  sol  est  moyennement  d’environ  126  millimetres 
(4'960  inches)  par  siecle.” 
L 2 
