﻿NOTES 
  ON 
  A 
  JOURNEY 
  FROM 
  ALGIERS 
  TO 
  THE 
  SAHARA. 
  105 
  

  

  15. 
  Geological 
  Notes 
  on 
  a 
  Journey 
  from 
  Algiers 
  to 
  the 
  Sahara. 
  

   By 
  George 
  Maw, 
  Esq., 
  F.G.S. 
  &c. 
  (Read 
  February 
  52, 
  1874.) 
  

  

  [Plate 
  XI.] 
  

  

  During 
  the 
  spring 
  of 
  1873 
  I 
  paid 
  a 
  short 
  visit 
  to 
  the 
  province 
  of 
  

   Algiers, 
  and 
  beg 
  to 
  lay 
  before 
  the 
  Society 
  the 
  result 
  of 
  my 
  observa- 
  

   tions 
  on 
  the 
  main 
  geological 
  features 
  of 
  the 
  district 
  between 
  Algiers 
  

   and 
  the 
  Sahara. 
  

  

  The 
  military 
  road 
  running 
  almost 
  due 
  north 
  and 
  south 
  from 
  the 
  

   Mediterranean 
  coast 
  of 
  Algiers 
  to 
  the 
  borders 
  of 
  the 
  desert 
  at 
  

   L'Aghouat, 
  the 
  most 
  southern 
  French 
  military 
  outpost, 
  and 
  crossing 
  

   nearly 
  at 
  right 
  angles 
  the 
  prevalent 
  line 
  of 
  strike 
  and 
  trend 
  of 
  the 
  

   high 
  and 
  low 
  ground, 
  suggested 
  itself 
  to 
  me 
  as 
  affording 
  the 
  most 
  

   comprehensive 
  section 
  in 
  a 
  continuous 
  line 
  that 
  could 
  be 
  selected 
  for 
  

   my 
  object, 
  which 
  was 
  to 
  compare 
  the 
  geological 
  features 
  of 
  Algeria 
  

   with 
  those 
  of 
  Marocco 
  observed 
  during 
  my 
  visits 
  to 
  that 
  country 
  in 
  

   the 
  years 
  1869 
  and 
  1871. 
  

  

  Very 
  little 
  has 
  heretofore 
  been 
  written 
  about 
  the 
  geology 
  of 
  Algeria 
  ; 
  

   and, 
  indeed, 
  the 
  best 
  published 
  maps 
  fall 
  short 
  of 
  giving 
  a 
  correct 
  

   delineation 
  of 
  even 
  the 
  hill- 
  and 
  valley- 
  systems 
  of 
  the 
  country. 
  

  

  My 
  line 
  of 
  route 
  of 
  285 
  miles 
  and 
  3° 
  of 
  latitude 
  (viz. 
  from 
  36° 
  47' 
  

   N. 
  to 
  33° 
  48' 
  X., 
  or 
  a 
  trifle 
  over 
  210 
  miles 
  in 
  a 
  direct 
  line) 
  included 
  

   30 
  miles 
  by 
  rail, 
  from 
  Algiers 
  to 
  Blidah, 
  thence 
  lay 
  diligence 
  over 
  the 
  

   Lesser 
  Atlas, 
  through 
  the 
  gorge 
  of 
  La 
  Chiffa 
  to 
  Medeah, 
  and 
  thence 
  

   over 
  the 
  high 
  land 
  of 
  the 
  Tell 
  to 
  Boukhari, 
  along 
  a 
  well-engineered 
  

   road 
  which 
  at 
  present 
  terminates 
  at 
  a 
  point 
  about 
  110 
  miles 
  from 
  

   Algiers 
  (See 
  Map, 
  PI. 
  XL). 
  From 
  Boukhari 
  to 
  L'Aghouat, 
  for 
  the 
  

   remaining 
  200 
  miles 
  over 
  the 
  Salt 
  Plains 
  and 
  Hauts 
  Plateaux, 
  com- 
  

   munication 
  is 
  kept 
  up 
  by 
  a 
  small 
  omnibus, 
  running 
  every 
  fifth 
  day 
  

   along 
  a 
  rough 
  track 
  almost 
  devoid 
  of 
  bridges, 
  little 
  better 
  than 
  a 
  

   caravan-route, 
  and 
  which 
  would 
  be 
  quite 
  impassable 
  to 
  ordinary 
  

   European 
  vehicles. 
  The 
  dotted 
  line 
  on 
  the 
  map 
  indicates 
  my 
  route, 
  

   and 
  the 
  black 
  line 
  the 
  section 
  represented 
  in 
  the 
  diagram 
  PI. 
  XL, 
  

   in 
  which 
  an 
  occasional 
  feature 
  lying 
  a 
  little 
  east 
  or 
  west 
  of 
  the 
  actual 
  

   line 
  of 
  section 
  has 
  been 
  introduced. 
  The 
  fine 
  double 
  lines 
  crossing 
  

   the 
  main 
  line 
  of 
  section 
  indicate 
  the 
  strike 
  of 
  the 
  beds. 
  

  

  In 
  general 
  terms 
  the 
  portion 
  of 
  Algeria 
  crossed 
  in 
  my 
  route 
  may 
  

   be 
  described 
  as 
  a 
  great 
  plateau 
  of 
  an 
  average 
  height 
  of 
  3000 
  feet, 
  

   bounded 
  on 
  the 
  north 
  by 
  the 
  range 
  of 
  the 
  Lesser 
  Atlas, 
  in 
  precisely 
  

   the 
  same 
  way 
  as 
  the 
  great 
  plateau 
  of 
  Spain 
  is 
  backed 
  up 
  on 
  its 
  

   north 
  side 
  by 
  the 
  Pyrenees, 
  and 
  shelving 
  off 
  to 
  the 
  north 
  in 
  slopes 
  

   and 
  terraces 
  to 
  the 
  sea-level 
  of 
  the 
  Sahara. 
  In 
  detail, 
  the 
  general 
  

   mass 
  must 
  be 
  viewed 
  as 
  a 
  series 
  of 
  high 
  plateaux, 
  separated 
  by 
  in- 
  

   tervening 
  plains 
  at 
  a 
  relatively 
  lower 
  level 
  ; 
  these 
  plains 
  appear 
  to 
  

   correspond 
  with 
  the 
  former 
  relative 
  level 
  of 
  the 
  Sahara 
  submergence, 
  

   their 
  present 
  height 
  indicating 
  the 
  subsequent 
  rise 
  of 
  the 
  land, 
  and 
  

   represent 
  a 
  great 
  Postpliocene 
  anticlinal, 
  to 
  which 
  the 
  more 
  ancient 
  

  

  