﻿338 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Apr. 
  27, 
  

  

  member 
  of 
  the 
  group 
  were 
  first 
  discovered 
  by 
  me 
  in 
  1SC)0, 
  in 
  the 
  

   form 
  of 
  casts, 
  at 
  the 
  top 
  of 
  the 
  much-altered 
  and 
  disrupted 
  strata 
  at 
  

   Doctor's 
  Brook. 
  The 
  prolific 
  portions 
  of 
  the 
  strata 
  of 
  this 
  section, 
  

   and 
  those 
  to 
  the 
  west 
  of 
  it, 
  were 
  only 
  discovered 
  by 
  me 
  during* 
  the 
  

   past 
  summer. 
  In 
  the 
  red-limestone 
  beds 
  of 
  our 
  section 
  the 
  fossils 
  

   are 
  abundant 
  and 
  in 
  good 
  preservation. 
  

  

  The 
  following 
  are 
  the 
  principal 
  genera, 
  &c, 
  of 
  this 
  group 
  : 
  — 
  

   Orthoceras 
  (3 
  species); 
  several 
  species 
  of 
  Murchisonia, 
  Slrophomena, 
  

   Ortliis, 
  and 
  RhynclwneJla 
  ; 
  Calymene, 
  Crinoidea, 
  Oomulites, 
  Tent 
  a 
  - 
  

   culites, 
  Petraia 
  (Forresteri, 
  Salt.), 
  and 
  Pttraia, 
  sp. 
  

  

  The 
  lithological 
  characters 
  of 
  A 
  and 
  B 
  of 
  the 
  section 
  are 
  so 
  differ- 
  

   ent 
  that 
  there 
  is 
  not 
  the 
  least 
  difficulty 
  in 
  determining 
  the 
  termi- 
  

   nation 
  of 
  the 
  one 
  and 
  the 
  commencement 
  of 
  the 
  other. 
  

  

  Strata 
  A, 
  where 
  little 
  altered, 
  are 
  generally 
  hard, 
  slaty, 
  grey, 
  

   argillaceous, 
  and 
  arenaceous, 
  and 
  therefore 
  assume 
  the 
  variety 
  of 
  

   aspect 
  already 
  referred 
  to 
  when 
  altered. 
  Strata 
  B 
  are 
  in 
  the 
  lower 
  

   part 
  shaly, 
  black, 
  ferruginous, 
  and 
  argillaceous, 
  and 
  in 
  the 
  upper 
  

   part 
  they 
  are 
  finely 
  laminated. 
  The 
  horizontal 
  section 
  of 
  them 
  in 
  

   the 
  cove, 
  which 
  can 
  generally 
  be 
  seen 
  only 
  at 
  ebb-tide, 
  is 
  so 
  black, 
  

   that 
  it 
  has 
  often 
  been 
  considered 
  by 
  the 
  people 
  of 
  the 
  district 
  to 
  

   indicate 
  the 
  existence 
  of 
  coal. 
  A 
  singular 
  and 
  characteristic 
  feature 
  

   of 
  these 
  rocks 
  is 
  the 
  occurrence 
  of 
  concretions, 
  lying 
  often 
  in 
  beds 
  

   conformable 
  with 
  the 
  stratification, 
  and 
  contrasting 
  strikingly 
  with 
  

   the 
  finely 
  laminated 
  shale 
  in 
  which 
  they 
  are 
  enclosed. 
  These 
  occur 
  

   from 
  the 
  beginning 
  to 
  the 
  end 
  of 
  the 
  horizontal 
  section 
  in 
  the 
  cove, 
  

   for 
  a 
  length 
  of 
  about 
  1848 
  feet. 
  They 
  also 
  occur 
  in 
  the 
  vertical 
  

   section 
  of 
  the 
  same 
  strata 
  at 
  Doctor's 
  Brook, 
  and 
  at 
  Arisaig 
  Pier, 
  

   or 
  through 
  a 
  total 
  length 
  of 
  about 
  two 
  miles. 
  The 
  conditions 
  

   under 
  which 
  strata 
  B 
  have 
  been 
  formed 
  appear 
  not 
  to 
  have 
  been 
  of 
  

   the 
  kind 
  most 
  favourable 
  for 
  the 
  existence 
  and 
  development 
  of 
  life. 
  

   The 
  thickness 
  of 
  strata 
  exposed 
  in 
  the 
  line 
  of 
  section 
  is 
  170 
  feet, 
  yet, 
  

   after 
  a 
  diligent 
  search, 
  I 
  only 
  found 
  a 
  few 
  Linr/ulce 
  in 
  nodules, 
  and 
  a 
  

   specimen 
  in 
  one 
  of 
  the 
  concretions 
  already 
  referred 
  to, 
  and 
  one 
  or 
  two 
  

   remarkable 
  beds 
  of 
  Graptolites; 
  of 
  the 
  latter 
  I 
  extracted 
  several 
  

   hundred 
  specimens, 
  more 
  or 
  less 
  perfect. 
  These 
  Graptolites 
  are 
  of 
  

   five 
  or 
  six 
  forms, 
  all 
  different 
  from 
  Graptolithus 
  CUntonensis, 
  disco- 
  

   vered 
  by 
  Dr. 
  Dawson 
  in 
  the 
  beds 
  above 
  the 
  portion 
  of 
  the 
  series 
  

   under 
  consideration. 
  In 
  the 
  line 
  of 
  section 
  we 
  have 
  also, 
  be) 
  T 
  ond 
  

   doubt, 
  the 
  upper 
  members 
  of 
  the 
  series 
  B', 
  C, 
  D 
  of 
  the 
  other 
  sections, 
  

   obscured 
  by 
  drift. 
  I 
  found 
  characteristic 
  fossils 
  of 
  C, 
  the 
  equivalent 
  

   of 
  the 
  Aymestry 
  limestone, 
  at 
  Doctor's 
  Brook, 
  and 
  of 
  B' 
  in 
  a 
  very 
  

   small 
  brook 
  to 
  the 
  west 
  of 
  the 
  Frenchman's 
  Barn 
  ; 
  and 
  in 
  surface- 
  

   stones 
  in 
  the 
  line 
  of 
  section 
  I 
  found 
  several 
  specimens 
  of 
  Avicula 
  

   Honeymani, 
  Hall, 
  which 
  is 
  only 
  found 
  in 
  D 
  of 
  the 
  series, 
  or 
  the 
  

   equivalent 
  of 
  the 
  Ludlow 
  Tilestone. 
  At 
  the 
  side 
  of 
  Doctor's 
  Brook, 
  

   in 
  the 
  same 
  line, 
  is 
  a 
  bluff, 
  which 
  has 
  only 
  yet 
  yielded 
  a 
  few 
  

   Lingulce 
  ; 
  they 
  are 
  not 
  characteristic 
  species. 
  We 
  have 
  then 
  another 
  

   part 
  of 
  the 
  group, 
  which 
  is 
  also 
  obscure. 
  This 
  is 
  possibly 
  a 
  repeti- 
  

   tion 
  of 
  B' 
  of 
  the 
  series. 
  The 
  strata 
  of 
  the 
  bluff, 
  as 
  well 
  as 
  of 
  B' 
  (?). 
  

   dip 
  towards 
  the 
  north; 
  and 
  so 
  do 
  the 
  others 
  on 
  this 
  side, 
  as 
  has 
  

  

  