﻿108 
  GEORGE 
  MAW'S 
  NOTES 
  ON 
  A 
  JOTTRNET 
  

  

  rocks 
  ; 
  nor 
  did 
  I 
  observe 
  a 
  single 
  eruptive 
  rock 
  on 
  the 
  line 
  of 
  section 
  

   from 
  Algiers 
  to 
  L'Aghouat. 
  

  

  At 
  the 
  foot 
  of 
  the 
  Lesser 
  Atlas, 
  flanking 
  the 
  Mitidja, 
  small 
  

   isolated 
  fragments 
  of 
  Tertiary 
  beds 
  are 
  seen 
  clinging 
  to 
  the 
  older 
  

   rocks, 
  and, 
  it 
  is 
  probable, 
  were 
  once 
  continuous 
  with 
  the 
  Tertiary 
  beds 
  

   on 
  the 
  north 
  side 
  of 
  the 
  plain 
  near 
  Algiers; 
  as 
  these 
  fragments, 
  both 
  

   at 
  the 
  back 
  of 
  Blidah 
  and 
  at 
  the 
  entrance 
  of 
  the 
  gorge 
  of 
  La 
  Chiffa, 
  

   run 
  up 
  into 
  the 
  Atlas 
  valleys, 
  they 
  must 
  have 
  been 
  deposited 
  since 
  

   the 
  Atlas 
  assumed 
  its 
  existing 
  contour. 
  

  

  The 
  central 
  mass 
  of 
  the 
  range, 
  exposed 
  in 
  a 
  number 
  of 
  sections 
  in 
  

   the 
  gorge 
  of 
  La 
  Chiffa, 
  consists 
  of 
  a 
  hard, 
  close-grained, 
  dark 
  blue, 
  

   argillaceous 
  rock, 
  commencing 
  with 
  a 
  small 
  anticlinal 
  at 
  the 
  entrance 
  

   of 
  the 
  gorge, 
  and 
  then 
  dipping 
  south 
  at 
  a 
  high 
  angle, 
  averaging 
  from 
  

   50° 
  to 
  60° 
  and 
  occasionally 
  70°, 
  or 
  almost 
  vertical, 
  with 
  a 
  strike 
  

   nearly 
  east 
  and 
  west, 
  corresponding 
  with 
  the 
  trend 
  of 
  the 
  chain. 
  

   The 
  rock 
  is 
  here 
  and 
  there 
  slightly 
  cleaved, 
  the 
  cleavage 
  being 
  nearly 
  

   coincident 
  with 
  the 
  stratification. 
  

  

  At 
  first 
  sight 
  the 
  Atlas 
  rocks 
  appear 
  to 
  be 
  a 
  distinct 
  series 
  from 
  

   those 
  forming 
  the 
  base 
  of 
  the 
  Tell 
  plateau 
  ; 
  but 
  after 
  a 
  careful 
  

   working-out 
  of 
  this 
  part 
  of 
  the 
  section, 
  I 
  think 
  it 
  probable 
  that 
  they 
  

   are 
  merely 
  an 
  altered 
  condition 
  of 
  the 
  lower 
  members 
  of 
  the 
  great 
  

   series 
  of 
  Mesozoic 
  beds 
  (probably 
  of 
  Cretaceous 
  age), 
  of 
  which 
  the 
  

   Tell 
  and 
  the 
  Hauts 
  Plateaux 
  are 
  composed, 
  the 
  prevailing 
  character 
  

   of 
  which 
  resembles 
  that 
  of 
  our 
  Lower 
  Lias. 
  On 
  the 
  north 
  side 
  of 
  

   the 
  range, 
  strata 
  of 
  this 
  aspect 
  are 
  seen 
  in 
  the 
  bed 
  of 
  the 
  stream 
  by 
  

   the 
  first 
  bridge 
  south 
  of 
  Blidah, 
  and 
  are 
  replaced 
  a 
  mile 
  further 
  south 
  

   by 
  the 
  more 
  slaty 
  rock 
  of 
  the 
  Atlas, 
  with 
  a 
  similar 
  strike 
  and 
  dip. 
  

   Again, 
  at 
  the 
  south 
  end 
  of 
  the 
  gorge 
  of 
  La 
  Chiffa 
  the 
  slaty 
  rock 
  gra- 
  

   duates 
  into 
  stratified 
  alternations 
  of 
  hard 
  bands 
  with 
  intervening 
  

   clayey 
  shales 
  ; 
  and 
  these, 
  between 
  the 
  south 
  end 
  of 
  the 
  gorge 
  and 
  

   Medeah, 
  give 
  place 
  to 
  a 
  great 
  mass 
  of 
  grey 
  marly 
  shales, 
  here 
  and 
  

   there 
  somewhat 
  schistose, 
  which 
  are 
  seen 
  to 
  underlie 
  the 
  Tertiary 
  

   series 
  forming 
  the 
  capping 
  of 
  the 
  Tell. 
  

  

  The 
  Plateau 
  of 
  the 
  Tell 
  consists 
  of 
  an 
  irregular 
  tableland, 
  of 
  an 
  

   average 
  height 
  of 
  3500 
  feet, 
  about 
  30 
  miles 
  across, 
  extending 
  

   from 
  the 
  Lesser 
  Atlas 
  on 
  its 
  northern 
  boundary 
  to 
  Boghar 
  on 
  its 
  

   southern 
  escarpment. 
  In 
  ascending 
  from 
  the 
  gorge 
  of 
  La 
  Chiffa, 
  the 
  

   Mesozoic 
  grey 
  shales 
  and 
  marls 
  are 
  lost, 
  and 
  the 
  capping 
  of 
  the 
  

   northern 
  half 
  of 
  the 
  Tell 
  is 
  seen 
  to 
  consist 
  of 
  a 
  Tertiary 
  series 
  ex- 
  

   tending 
  about 
  14 
  miles 
  from 
  Medeah 
  to 
  within 
  a 
  mile 
  of 
  Berou- 
  

   agui'a, 
  as 
  an 
  irregular 
  undulating 
  synclinal, 
  presenting 
  a 
  series 
  of 
  

   escarpments 
  at 
  its 
  northern 
  and 
  southern 
  boundary 
  respectively, 
  

   facing 
  north 
  and 
  south, 
  and 
  including 
  bright 
  red 
  marls 
  resting 
  on 
  

   the 
  Mesozoic 
  rocks, 
  overlain 
  by 
  calcareous 
  freestones 
  containing 
  

   fossils, 
  interstratified 
  with 
  grey 
  and 
  variegated 
  marls, 
  the 
  whole 
  

   having 
  a 
  collective 
  thickness 
  of 
  from 
  300 
  to 
  500 
  feet. 
  The 
  fossils 
  

   are 
  very 
  obscure, 
  most 
  of 
  them 
  occurring 
  only 
  as 
  casts, 
  and 
  few 
  of 
  

   the 
  species 
  are 
  determinable. 
  Mr. 
  Etheridge 
  has 
  determined 
  the 
  

   following 
  genera, 
  and 
  from 
  their 
  general 
  facies 
  thinks 
  the 
  series 
  

   may 
  include 
  beds 
  of 
  both 
  Pliocene 
  and 
  Miocene 
  age, 
  viz. 
  Solen, 
  

  

  