﻿FROM 
  ALGIERS 
  TO 
  THE 
  SAHARA. 
  121 
  

  

  the 
  northern 
  Sahara 
  plain 
  at 
  a 
  height 
  of 
  2700 
  feet, 
  and 
  on 
  the 
  open 
  

   Sahara 
  south 
  of 
  the 
  Hauts 
  Plateaux 
  at 
  a 
  height 
  of 
  from 
  2700 
  to 
  3000 
  

   feet, 
  as 
  well 
  as 
  the 
  coast-denudation 
  of 
  the 
  flat-topped 
  sandstone 
  

   hills 
  at 
  Sidi 
  Makhelouf 
  at 
  a 
  height 
  of 
  2700 
  feet. 
  

  

  At 
  this 
  time 
  the 
  Algerian 
  promontory 
  was 
  an 
  island, 
  separated 
  

   from 
  the 
  Atlas 
  and 
  Tell 
  by 
  a 
  strait 
  six 
  or 
  seven 
  miles 
  wide, 
  now 
  the 
  

   plain 
  of 
  the 
  Mitidja. 
  The 
  Lesser 
  Atlas 
  rose 
  directly 
  from 
  the 
  sea, 
  

   into 
  which 
  its 
  streams 
  were 
  bringing 
  down 
  subaerial 
  debris, 
  and 
  

   depositing 
  the 
  great 
  delta-like 
  mass 
  of 
  drift 
  on 
  which 
  Blidah 
  is 
  built. 
  

   Crossing 
  the 
  Atlas 
  and 
  Tell 
  we 
  should 
  soon 
  reach 
  another 
  inland 
  

   sea 
  some 
  fifty 
  miles 
  wide, 
  now 
  represented 
  by 
  the 
  north 
  Sahara 
  

   plain, 
  out 
  of 
  which 
  the 
  range 
  of 
  the 
  Djebel 
  Sahari 
  rose 
  as 
  a 
  chain 
  

   of 
  islands 
  ; 
  and 
  its 
  southern 
  limit 
  is 
  now 
  well 
  recorded' 
  by 
  the 
  long 
  

   range 
  of 
  sandhills 
  on 
  the 
  southern 
  margin 
  of 
  the 
  plain 
  nortb 
  of 
  the 
  

   Hauts 
  Plateaux. 
  The 
  Hauts 
  Plateaux 
  formed 
  another 
  range 
  of 
  

   isolated 
  land 
  running 
  nearly 
  east 
  and 
  west, 
  30 
  miles 
  wide 
  ; 
  and 
  on 
  its 
  

   southern 
  side 
  fjords 
  ran 
  up 
  among 
  the 
  valleys 
  and 
  debouched 
  at 
  

   LAghouat 
  into 
  the 
  open 
  Sahara 
  sea, 
  some 
  800 
  miles 
  across, 
  which 
  

   separated 
  by 
  a 
  broad 
  expanse 
  of 
  water 
  the 
  islands 
  of 
  the 
  Tell 
  and 
  

   Hauts 
  Plateaux 
  from 
  the 
  highlands 
  of 
  Central 
  Africa. 
  

  

  (8) 
  ReeUvation 
  of 
  the 
  Land. 
  — 
  An 
  upward 
  movement 
  followed 
  the 
  

   Sahara 
  submergence, 
  the 
  extreme 
  limit 
  of 
  which, 
  whether 
  repre- 
  

   sented 
  by 
  the 
  present 
  height 
  of 
  the 
  land, 
  or 
  attaining 
  a 
  higher 
  level, 
  

   is 
  open 
  to 
  question. 
  It 
  is, 
  however, 
  certain 
  that 
  an 
  emergence 
  of 
  

   the 
  highlands 
  of 
  Algeria 
  took 
  place 
  to 
  the 
  extent 
  of 
  about 
  3000 
  feet; 
  

   but 
  the 
  reelevation 
  appears 
  to 
  have 
  been 
  greatest 
  to 
  the 
  south 
  of 
  

   the 
  chain 
  of 
  the 
  Lesser 
  Atlas. 
  The 
  contour 
  of 
  the 
  limit 
  of 
  elevation, 
  

   as 
  indicated 
  by 
  the 
  present 
  level 
  of 
  the 
  marine 
  deposits 
  of 
  the 
  Mitidja 
  

   and 
  Sahara 
  plains, 
  would 
  represent 
  a 
  wide 
  low 
  anticlinal, 
  gradually 
  

   rising 
  from 
  the 
  sea-level 
  at 
  Algiers 
  across 
  the 
  plain 
  of 
  the 
  Mitidja 
  

   to 
  a 
  height 
  of 
  2700 
  feet 
  at 
  the 
  north 
  side 
  of 
  the 
  Hauts 
  Plateaux, 
  and 
  

   then 
  descending 
  from 
  2700 
  feet 
  on 
  its 
  south 
  side 
  to 
  the 
  sea-level 
  in 
  

   the 
  open 
  Sahara. 
  The 
  extent 
  of 
  the 
  elevation 
  following 
  the 
  sub- 
  

   mergence 
  of 
  the 
  Sahara, 
  is 
  a 
  question 
  of 
  considerable 
  interest. 
  In 
  

   a 
  former 
  paper 
  read 
  before 
  the 
  Society, 
  and 
  in 
  a 
  paper 
  read 
  before 
  

   the 
  British 
  Association 
  at 
  Liverpool, 
  I 
  recorded 
  several 
  facts 
  in 
  proof 
  

   that 
  the 
  present 
  coast-line 
  of 
  the 
  Mediterranean, 
  in 
  several 
  far- 
  

   removed 
  localities, 
  is 
  gradually 
  subsiding 
  ; 
  and 
  Mr. 
  Boyd 
  Dawkins, 
  

   in 
  his 
  paper 
  on 
  the 
  physical 
  geography 
  of 
  the 
  Mediterranean, 
  has 
  

   on 
  palaeontological 
  and 
  other 
  evidence 
  pointed 
  out 
  the 
  probability 
  

   that 
  during 
  the 
  Pleistocene 
  age 
  the 
  land 
  now 
  forming 
  its 
  shore- 
  

   line 
  stood 
  at 
  a 
  height 
  of 
  about 
  3000 
  feet 
  above 
  its 
  present 
  level. 
  

   Again, 
  moraines 
  were 
  observed 
  by 
  Dr. 
  Hooker, 
  Mr. 
  Ball, 
  and 
  myself 
  

   in 
  the 
  Great 
  Atlas 
  south 
  of 
  Marocco, 
  at 
  a 
  height 
  of 
  from 
  6000 
  to 
  

   7000 
  feet, 
  in 
  a 
  latitude 
  where 
  no 
  perpetual 
  snow 
  now 
  lies 
  at 
  .12,000 
  

   feet 
  ; 
  so 
  it 
  is 
  probable 
  that 
  the 
  land 
  stood 
  at 
  a 
  much 
  greater 
  eleva- 
  

   tion 
  when 
  these 
  moraines 
  were 
  formed. 
  

  

  On 
  the 
  other 
  hand, 
  Sir 
  C. 
  Lyell 
  has 
  suggested 
  that 
  the 
  former 
  

   diminution 
  of 
  temperature 
  and 
  extension 
  to 
  lower 
  levels 
  of 
  alpine 
  

   glaciers 
  was 
  probably 
  the 
  result 
  of 
  diminished 
  temperature 
  duo 
  to 
  

  

  