﻿588 
  DE. 
  W. 
  TEASER 
  HUME 
  ON 
  [Dec. 
  1897, 
  

  

  majority 
  of 
  the 
  mollusca 
  present 
  are 
  most 
  abundant 
  in 
  the 
  Ammo- 
  

   nites 
  inflatus-heds 
  of 
  the 
  West 
  of 
  England 
  — 
  for 
  example, 
  Hoplites 
  

   catillus, 
  Sow., 
  Cucullcea 
  carinata, 
  Sow., 
  and 
  the 
  large 
  dimyarian 
  

   bivalves. 
  In 
  the 
  Central 
  Division 
  no 
  member 
  of 
  a 
  fauna 
  character- 
  

   istically 
  later 
  than 
  this 
  zone 
  (the 
  zone 
  of 
  Ammonites 
  inflates 
  of 
  

   Barrois) 
  has 
  been 
  met 
  with, 
  but 
  the 
  brachiopoda 
  and 
  pectens 
  

   obtained 
  in 
  Islandmagee 
  suggest 
  the 
  probability 
  that 
  "Warminster 
  

   (Pecten 
  asper-zone) 
  conditions 
  had 
  already 
  commenced 
  in 
  the 
  deeper 
  

   waters 
  of 
  the 
  Eastern 
  Division. 
  

  

  In 
  connexion 
  with 
  this 
  latter 
  supposition 
  we 
  have 
  not 
  ourselves 
  

   noted 
  Ammonites 
  \8chloenbachicC\ 
  v 
  avians, 
  recorded 
  by 
  Tate 
  from 
  

   the 
  latter 
  district, 
  but 
  the 
  pectens 
  (subgenus 
  Chlamys) 
  obtained 
  

   were 
  P. 
  asper, 
  Lam., 
  P. 
  Galliennei, 
  d'Orb., 
  and 
  P. 
  hispidus, 
  Goldf. 
  

   Chlamys 
  is 
  therefore 
  abundant, 
  and 
  these 
  species 
  are 
  moi»e 
  common 
  

   in 
  the 
  Warminster 
  than 
  in 
  the 
  Devizes 
  beds 
  ; 
  it 
  must 
  also 
  be 
  

   admitted 
  that 
  the 
  Bhynchonellce 
  and 
  Tevebvatulce 
  accompanjdng 
  

   them 
  usually 
  occur 
  in 
  beds 
  younger 
  than 
  the 
  Ammonites 
  inflatus- 
  

   zone. 
  We 
  conclude 
  then 
  that 
  the 
  Glauconitic 
  Sands 
  commenced 
  

   during 
  the 
  earlier 
  period 
  of 
  the 
  Ammonites 
  inflatus-zone, 
  and, 
  owing 
  

   to 
  their 
  nearer 
  proximity 
  to 
  a 
  coast-line 
  than 
  the 
  Devon 
  Green 
  sands, 
  

   they 
  retain 
  a 
  strong 
  admixture 
  of 
  the 
  earlier 
  Blackdown 
  fauna, 
  

   though, 
  in 
  the 
  deeper-water 
  exposures, 
  containing 
  forms 
  which, 
  as 
  

   depression 
  proceeded 
  in 
  England, 
  became 
  dominant 
  in 
  the 
  upper 
  

   zone 
  of 
  the 
  English 
  greensand. 
  

  

  Murray 
  and 
  Eenard 
  1 
  have 
  given 
  an 
  account 
  of 
  the 
  general 
  mode 
  

   of 
  formation 
  of 
  glauconite, 
  pointing 
  out 
  that 
  it 
  is 
  along 
  high 
  and 
  

   bold 
  coasts, 
  where 
  no 
  rivers 
  enter 
  the 
  sea, 
  and 
  where 
  accumulation 
  

   is 
  apparently 
  less 
  rapid, 
  that 
  glauconite 
  appears 
  in 
  its 
  most 
  typical 
  

   form 
  and 
  greatest 
  abundance. 
  These 
  deposits 
  are 
  also 
  formed 
  near 
  

   continental 
  masses 
  of 
  land 
  about 
  the 
  lower 
  limits 
  of 
  wave-, 
  tidal, 
  

   and 
  current-action 
  : 
  that 
  is, 
  in 
  the 
  neighbourhood 
  of 
  Murray's 
  

   mud-line, 
  in 
  the 
  zone 
  of 
  maximum 
  chemical 
  activity. 
  

  

  The 
  Irish 
  rock 
  is 
  richer 
  in 
  glauconite 
  than 
  the 
  typical 
  examples 
  

   dredged 
  by 
  the 
  Challenger 
  Expedition, 
  the 
  nearest 
  approach 
  to 
  it 
  

   being 
  the 
  dark 
  greensand 
  obtained 
  by 
  the 
  TJ.S.S. 
  Tuscarora. 
  That 
  

   the 
  deposit 
  was 
  formed 
  near 
  land 
  seems 
  certain 
  from 
  the 
  great 
  

   numbers 
  of 
  the 
  pelecypoda, 
  their 
  existence 
  in 
  colonies, 
  and 
  their 
  

   large 
  size 
  ; 
  the 
  probability 
  of 
  a 
  high 
  coast-line 
  is 
  testified 
  by 
  the 
  

   abundance 
  of 
  glauconite, 
  and 
  comparatively 
  small 
  percentage 
  of 
  

   detrital 
  minerals. 
  The 
  chemical 
  action 
  is 
  evidenced 
  by 
  the 
  fre- 
  

   quency 
  of 
  casts, 
  especially 
  among 
  the 
  dimyaria 
  of 
  the 
  Central 
  

   Division. 
  As 
  these 
  deposits 
  do 
  not 
  continue 
  to 
  the 
  north 
  much 
  

   beyond 
  Larne, 
  and 
  to 
  the 
  south 
  disappear 
  at 
  Colin 
  Mountain, 
  it 
  

   would 
  seem 
  that 
  the 
  formation 
  was 
  laid 
  down 
  in 
  an 
  indentation 
  of 
  

   the 
  coast, 
  the 
  Central 
  Division 
  being 
  nearest 
  to 
  the 
  shore-line. 
  A 
  

   fauna 
  similar 
  to 
  that 
  of 
  the 
  highest 
  Blackdown 
  Beds 
  here 
  found 
  a 
  

   suitable 
  home, 
  and, 
  so 
  long 
  as 
  the 
  conditions 
  continued 
  favourable, 
  

   flourished 
  in 
  a 
  high 
  degree, 
  thus 
  becoming 
  contemporaneous 
  with 
  

   species 
  characteristic 
  of 
  higher 
  zones 
  in 
  England. 
  

  

  1 
  Challenger 
  Eeports, 
  ' 
  Deep-Sea 
  Deposits/ 
  p. 
  382. 
  

  

  