﻿FBOM 
  ALGIERS 
  TO 
  THE 
  SAHAEA. 
  Ill 
  

  

  tions, 
  which 
  are 
  conspicuous 
  from 
  a 
  great 
  distance. 
  Between 
  these 
  

   hills 
  and 
  the 
  northern 
  escarpment 
  of 
  the 
  Hauts 
  Plateaux, 
  the 
  low- 
  

   level 
  plain 
  continues 
  for 
  about 
  fifteen 
  miles, 
  first 
  descending 
  from 
  

   the 
  anticlinal 
  of 
  Guelt-el-stel 
  to 
  a 
  level 
  of 
  2550 
  feet, 
  and 
  then 
  gra- 
  

   dually 
  ascending 
  to 
  the 
  Eoeher 
  de 
  Sel 
  at 
  the 
  foot 
  of 
  the 
  Hauts 
  

   Plateaux, 
  at 
  a 
  height 
  of 
  2800 
  feet. 
  This 
  second 
  plain 
  appears 
  to 
  be 
  

   a 
  repetition, 
  dipping 
  south, 
  of 
  the 
  gypseous 
  and 
  saliferous 
  marls 
  of 
  

   A'in 
  Oussera, 
  on 
  the 
  north 
  side 
  of 
  the 
  Guelt-el-Stel 
  anticlinal. 
  Two 
  

   large 
  salt-lakes 
  (the 
  Sebka 
  Zahrez) 
  occur 
  at 
  a 
  height 
  of 
  2550 
  feet 
  in 
  

   the 
  plain, 
  a 
  little 
  to 
  the 
  south 
  of 
  the 
  Djebel 
  Sahari 
  ; 
  and 
  a 
  little 
  

   further 
  south 
  nitre 
  is 
  obtained 
  by 
  evaporation 
  from 
  square 
  pans 
  ex- 
  

   cavated 
  in 
  the 
  grey 
  marls. 
  

  

  The 
  plain 
  south 
  of 
  the 
  Djebel 
  Sahari 
  is 
  covered 
  with 
  a 
  deposit 
  of 
  

   grey 
  silty 
  loam, 
  before 
  referred 
  to 
  as 
  the 
  " 
  Sahara 
  loam 
  ;" 
  and 
  here 
  

   we 
  have 
  clear 
  evidence 
  of 
  recent 
  marine 
  submergence 
  in 
  the 
  occur- 
  

   rence 
  between 
  the 
  Djebel 
  Sahari 
  and 
  the 
  Hauts 
  Plateaux 
  of 
  an 
  ex- 
  

   tensive 
  range 
  of 
  sandhills. 
  I 
  am 
  also 
  informed 
  by 
  Mr. 
  Tristram 
  

   that 
  raised 
  beaches 
  of 
  concrete 
  shell-beds, 
  similar 
  to 
  those 
  on 
  the 
  

   coast, 
  occur 
  in 
  this 
  neighbourhood. 
  He 
  does 
  not 
  mention 
  their 
  

   altitude, 
  which, 
  however, 
  cannot 
  be 
  less 
  than 
  from 
  2000 
  to 
  2500 
  

   feet. 
  They 
  form 
  a 
  most 
  important 
  point 
  in 
  the 
  evidence 
  of 
  the 
  

   Sahara 
  submergence, 
  to 
  which 
  I 
  shall 
  have 
  to 
  make 
  further 
  

   reference. 
  

  

  The 
  Rockers 
  de 
  Sel, 
  or, 
  in 
  Arabic, 
  Hadjar 
  el 
  Mehl, 
  forming 
  the 
  

   first 
  and 
  most 
  northern 
  escarpment 
  of 
  the 
  Hauts 
  Plateaux, 
  rise 
  up 
  

   from 
  the 
  northern 
  boundary 
  of 
  the 
  plain, 
  which 
  here 
  attains 
  a 
  level 
  

   of 
  2850 
  feet 
  near 
  the 
  fifth 
  caravansary. 
  The 
  Iiochers 
  attain 
  a 
  further 
  

   height 
  of 
  300 
  or 
  400 
  feet, 
  and 
  present 
  a 
  strangely 
  weird 
  aspect. 
  

   The 
  mass 
  consists 
  of 
  dark 
  grey 
  marls, 
  mixed 
  with 
  rock-salt 
  and 
  

   gypsum, 
  and 
  interstratified 
  with 
  hard 
  grey 
  argillaceous 
  rock-bands, 
  

   the 
  whole 
  presenting 
  a 
  broken 
  and 
  tumbled 
  arrangement. 
  In 
  one 
  

   place 
  the 
  strike 
  is 
  nearly 
  north 
  and 
  south, 
  and 
  dip 
  nearly 
  vertical 
  ; 
  

   but 
  the 
  general 
  dip 
  and 
  strike 
  correspond, 
  as 
  far 
  as 
  I 
  could 
  ascertain, 
  

   with 
  the 
  general 
  dip 
  and 
  strike 
  of 
  the 
  northern 
  escarpments 
  of 
  the 
  

   Hauts 
  Plateaux, 
  the 
  beds 
  of 
  which 
  the 
  saliferous 
  marls 
  appear 
  to 
  

   underlie. 
  The 
  salt-mountain 
  is 
  capped 
  with 
  great 
  blocks 
  of 
  tumbled 
  

   rock 
  scattered 
  about 
  in 
  the 
  wildest 
  confusion, 
  the 
  placement 
  of 
  which 
  

   is 
  evidently 
  due 
  to 
  the 
  dissolution 
  of 
  the 
  intercalated 
  and 
  underlying 
  

   salt-marls 
  ; 
  and 
  I 
  am 
  inclined 
  to 
  think 
  that 
  the 
  irregular 
  dip 
  and 
  

   strike 
  of 
  the 
  beds 
  in 
  situ 
  has 
  been 
  materially 
  influenced 
  by 
  the 
  

   failure 
  of 
  support 
  from 
  the 
  dissolution 
  of 
  the 
  salt-rock, 
  just 
  as 
  in 
  

   some 
  glacial 
  beds 
  the 
  melting 
  of 
  intercalated 
  ice 
  is 
  supposed 
  to 
  have 
  

   brought 
  about 
  a 
  confused 
  and 
  contorted 
  arrangement. 
  From 
  these 
  

   beds 
  I 
  obtained 
  an 
  Ostrea 
  allied 
  to 
  O. 
  carinata. 
  Mr. 
  Tristram 
  has 
  

   given 
  me 
  two 
  specimens 
  of 
  Exogyra 
  sinuata 
  and 
  an 
  Ostrea 
  allied 
  to 
  

   O. 
  cyaihula 
  he 
  found 
  here 
  in 
  1860 
  ; 
  and 
  Mr. 
  Etheridge 
  thinks 
  they 
  

   are 
  of 
  Cretaceous 
  or 
  Neocomian 
  age. 
  

  

  The 
  Hauts 
  Plateaux. 
  — 
  Prom 
  the 
  south 
  of 
  the 
  Eochers 
  de 
  Sel, 
  the 
  

   ground 
  rapidly 
  rises 
  in 
  a 
  series 
  of 
  terraces, 
  forming 
  the 
  northern 
  

   escarpments 
  of 
  the 
  Hauts 
  Plateaux. 
  Immediatelv 
  to 
  the 
  south 
  of 
  

  

  k2 
  

  

  