﻿PROM 
  ALGIERS 
  TO 
  THE 
  SAHARA. 
  117 
  

  

  Hemiaster 
  or 
  Penaster, 
  resembling 
  Penaster 
  Fournelli, 
  from 
  the 
  Hip- 
  

   purite 
  limestone 
  (Brissus 
  ?), 
  Avicula, 
  Inoceramus, 
  Lucina, 
  Cardium, 
  

   Area, 
  Byssoarca, 
  Cardita, 
  Cyrena 
  ? 
  Cwullcea, 
  Clavatula, 
  &c. 
  These 
  

   stand 
  out 
  as 
  bosses 
  from 
  the 
  matrix, 
  with 
  a 
  weathered 
  black 
  surface, 
  

   and 
  look 
  like 
  blotches 
  of 
  black 
  mud 
  ; 
  the 
  colour 
  is 
  only 
  skin-deep, 
  

   the 
  mass 
  of 
  the 
  nodules 
  being 
  of 
  a 
  pale 
  grey. 
  They 
  are 
  excessively 
  

   hard 
  and 
  diffictilt 
  to 
  break, 
  and 
  probably 
  consist 
  of 
  ferruginous 
  chert. 
  

   The 
  view 
  from 
  the 
  summit 
  of 
  the 
  escarpment 
  is 
  very 
  singular. 
  

   To 
  the 
  south 
  the 
  eye 
  ranges 
  over 
  the 
  great 
  plain 
  interrupted 
  only 
  

   by 
  the 
  rocky 
  ridge 
  of 
  L'Aghouat 
  ; 
  looking 
  north 
  a 
  gentle 
  dip-slope 
  

   descends 
  to 
  the 
  flat 
  valley 
  about 
  a 
  mile 
  wide, 
  bounded 
  on 
  the 
  opposite 
  

   side 
  by 
  a 
  complementary 
  dip-slope, 
  with 
  a 
  repetition 
  in 
  reverse 
  of 
  the 
  

   beds 
  seen 
  in 
  ascending 
  the 
  first 
  escarpment. 
  The 
  second 
  ridge 
  is 
  

   soon 
  crossed 
  ; 
  and 
  on 
  descending 
  its 
  escarpment 
  facing 
  north, 
  another 
  

   flat 
  valley 
  about 
  a 
  mile 
  wide 
  is 
  reached, 
  bounded 
  on 
  its 
  opposite 
  side 
  

   by 
  an 
  escarpment 
  facing 
  S.E. 
  The 
  view 
  from 
  the 
  summits 
  of 
  these 
  

   ridges 
  presents 
  a 
  series 
  of 
  ranges 
  running 
  N.E. 
  by 
  S.W. 
  (Fig. 
  2), 
  nearly 
  

   buried 
  by 
  a 
  Posttertiary 
  deposit 
  of 
  grey 
  loam, 
  forming 
  flat 
  valleys 
  

   about 
  a 
  mile 
  wide, 
  each 
  alternate 
  valley 
  occurring 
  between 
  dip-slopes 
  

   and 
  in 
  the 
  centre 
  of 
  a 
  denuded 
  anticlinal, 
  suggesting 
  to 
  the 
  eye 
  the 
  

   levelling 
  up 
  by 
  a 
  recent 
  deposit 
  of 
  a 
  series 
  of 
  hills 
  and 
  valleys 
  that 
  

   had 
  originally 
  been 
  of 
  greater 
  height 
  and 
  depth. 
  The 
  level 
  valley- 
  

   bottoms 
  of 
  loam 
  are 
  obviously 
  an 
  inland 
  extension 
  of 
  the 
  plain, 
  and 
  

   were 
  deposited 
  when 
  the 
  Sahara 
  sea 
  ran 
  up 
  as 
  fjords 
  between 
  the 
  

   promontories 
  of 
  older 
  land 
  that 
  branched 
  out 
  from 
  the 
  isolated 
  land 
  

   of 
  Algeria. 
  

  

  Lignite 
  occurs 
  in 
  several 
  localities 
  N. 
  of 
  L'Aghouat, 
  viz. 
  in 
  the 
  

   Djebel 
  Amour 
  at 
  Kusra 
  and 
  at 
  Berich, 
  also 
  at 
  El 
  Kheicha 
  on 
  the 
  banks 
  

   of 
  the 
  Oued 
  M'Zi, 
  a 
  branch 
  of 
  the 
  L'Aghouat 
  river, 
  where 
  it 
  is 
  a 
  

   metre 
  thick, 
  and 
  overlain 
  by 
  black 
  rock 
  ; 
  but 
  I 
  had 
  not 
  an 
  opportu- 
  

   nity 
  of 
  seeing 
  it 
  in 
  situ. 
  Fossil 
  plants 
  are 
  said 
  to 
  occur 
  a 
  day's 
  

   iourney 
  N.W. 
  of 
  L'Aghouat, 
  and 
  are 
  probably 
  associated 
  with 
  the 
  

   lignite 
  formation. 
  The 
  only 
  locality 
  where 
  the 
  lignite 
  has 
  been 
  

   observed 
  in 
  situ 
  by 
  a 
  geologist 
  is 
  that 
  noticed 
  by 
  Mr. 
  Tristram 
  at 
  

   Ai'n-el-Ibel, 
  where 
  it 
  occurs 
  near 
  the 
  horizon 
  of 
  the 
  band 
  of 
  bright 
  

   red 
  and 
  green 
  marls 
  exposed 
  in 
  several 
  localities 
  on 
  my 
  line 
  of 
  section, 
  

   and 
  probably 
  a 
  little 
  above 
  the 
  horizon 
  of 
  the 
  salt 
  deposit 
  of 
  the 
  

   Eochers 
  de 
  Sel. 
  

  

  Of 
  the 
  occurrence 
  of 
  other 
  minerals, 
  the 
  following 
  localities 
  were 
  

   named 
  to 
  me 
  at 
  L'Aghouat 
  : 
  — 
  

  

  Nitrate 
  of 
  potash 
  is 
  found 
  near 
  Touat, 
  manganese 
  at 
  Outhed 
  el 
  

   Abiod, 
  lead 
  at 
  Oued 
  Sidi 
  Bilgassem, 
  and 
  copper 
  at 
  Berich 
  ; 
  but 
  I 
  

   could 
  not 
  ascertain 
  the 
  mineralogical 
  conditions 
  under 
  which 
  the 
  lead 
  

   and 
  copper 
  occur. 
  

  

  My 
  return 
  journey 
  from 
  L'Aghouat, 
  following 
  the 
  same 
  line 
  of 
  

   route, 
  enabled 
  me 
  to 
  check 
  and 
  correct 
  the 
  altitudes 
  and 
  fill 
  in 
  addi- 
  

   tional 
  details 
  in 
  the 
  section. 
  

  

  Stratigraphical 
  Summary. 
  — 
  In 
  conclusion 
  I 
  will 
  give 
  a 
  general 
  

   summary 
  in 
  stratigraphical 
  sequence 
  of 
  the 
  formations 
  and 
  of 
  the 
  

   successive 
  changes 
  of 
  level 
  and 
  contour 
  of 
  the 
  district 
  comprised 
  in 
  

  

  