﻿602 
  DR. 
  W. 
  ERASER 
  HUME 
  ON 
  [Dec. 
  1897, 
  

  

  for 
  example, 
  the 
  Eocogyra 
  columba-, 
  Waldheimia 
  hibernica-, 
  and 
  

   Callianassa-hsnads), 
  while 
  a 
  noticeable 
  feature 
  is 
  the 
  frequent 
  

   occurrence 
  of 
  the 
  teeth 
  of 
  fishes 
  (Lanmidse 
  and 
  Hyliobatidse) 
  in 
  

   the 
  softer 
  sands 
  of 
  the 
  same 
  zone. 
  

  

  I 
  have 
  already 
  discussed 
  the 
  relation 
  of 
  a 
  rich 
  fish-fauna 
  to 
  

   currents 
  as 
  follows 
  : 
  — 
  ' 
  The 
  current 
  will 
  evidently 
  carry 
  along 
  

   with 
  it 
  large 
  amounts 
  of 
  material 
  derived 
  from 
  the 
  littoral 
  area, 
  

   and 
  far 
  more 
  suitable 
  to 
  a 
  piscine 
  palate 
  than 
  the 
  usual 
  minute 
  

   pelagic 
  fauna 
  of 
  an 
  oceanic 
  region. 
  The 
  result 
  would 
  be 
  that 
  

   comparatively 
  shallow-water 
  Teleostean 
  fishes, 
  such 
  as 
  Beryx, 
  

   would 
  have 
  their 
  range 
  greatly 
  extended, 
  .... 
  whilst 
  the 
  rich 
  

   increase 
  in 
  food-material 
  would 
  tend 
  to 
  bring 
  together 
  large 
  

   numbers 
  of 
  predatory 
  fishes, 
  especially 
  sharks, 
  such 
  as 
  Lamina, 
  etc. 
  

   In 
  this 
  way, 
  perhaps, 
  the 
  discovery 
  of 
  such 
  a 
  rich 
  fauna 
  may 
  be 
  

   explained.' 
  l 
  The 
  same 
  statements 
  appear 
  to 
  apply 
  to 
  the 
  case 
  under 
  

   consideration, 
  and 
  in 
  addition 
  it 
  should 
  be 
  noted 
  that 
  the 
  associated 
  

   mollusca 
  are 
  distinctly 
  littoral. 
  

  

  In 
  the 
  Inoceraimis-zone 
  the 
  new 
  fauna 
  also 
  appears 
  in 
  bands, 
  but 
  

   here 
  the 
  incoming 
  species 
  have 
  a 
  deeper-water 
  aspect, 
  and 
  the 
  beds 
  

   containing 
  them 
  yield 
  but 
  few 
  fish-remains. 
  

  

  Just 
  as 
  in 
  the 
  Central 
  Division, 
  it 
  is 
  below 
  the 
  unconformable 
  

   junction 
  that 
  current-action 
  is 
  most 
  suggested, 
  so 
  also 
  above 
  it 
  there 
  

   is 
  strong 
  evidence 
  pointing 
  in 
  the 
  same 
  direction. 
  Ground-currents 
  

   must 
  have 
  been 
  especially 
  active 
  during 
  the 
  period 
  of 
  the 
  Belemnitella 
  

   \_Actinocamax~\ 
  vera 
  and 
  B. 
  [A.~\ 
  quadrata-zon.es, 
  judging 
  from 
  the 
  

   extraordinary 
  admixture 
  of 
  the 
  older 
  and 
  younger 
  beds 
  at 
  their 
  

   junction, 
  the 
  nodular 
  or 
  conglomeratic 
  character 
  of 
  the 
  strata 
  imme- 
  

   diately 
  overlying 
  the 
  unconformity, 
  and 
  the 
  large 
  size 
  of 
  the 
  detrital 
  

   materials. 
  

  

  The 
  following 
  appear 
  to 
  have 
  been 
  the 
  principal 
  currents: 
  — 
  

   (1) 
  One 
  resulting 
  from 
  the 
  changes 
  which 
  ushered 
  in 
  the 
  Cenomanian 
  

   period, 
  extending 
  the 
  range 
  of 
  a 
  southern 
  fauna 
  northward, 
  and 
  

   accompanied 
  in 
  its 
  course 
  by 
  a 
  number 
  of 
  predatory 
  fishes. 
  (2) 
  One 
  

   commencing 
  at 
  the 
  beginning 
  of 
  the 
  Senonian, 
  setting 
  in 
  from 
  the 
  

   oceanic 
  areas 
  towards 
  land, 
  and 
  introducing 
  the 
  deep-sea 
  fauna, 
  

   unaccompanied 
  by 
  a 
  prominent 
  fish-fauna. 
  (3) 
  An 
  indefinite 
  current- 
  

   system, 
  resulting 
  from 
  the 
  submergence 
  of 
  the 
  prominent 
  land- 
  

   masses, 
  and 
  coincident 
  in 
  time 
  with 
  the 
  Belemnitella 
  [Actinocamax~] 
  

   vera- 
  or 
  Marsupites-zone. 
  This 
  gives 
  rise 
  to 
  marked 
  lithological 
  

   disturbances 
  and 
  unconformities, 
  and 
  may 
  have 
  been 
  synchronous 
  

   with 
  the 
  deposition 
  of 
  the 
  phosphatic 
  chalks 
  and 
  nodular 
  bands 
  

   common 
  in 
  many 
  Cretaceous 
  districts 
  at 
  this 
  horizon. 
  

  

  6. 
  Eeference 
  may 
  now 
  be 
  made 
  to 
  the 
  relation 
  of 
  spongiarian 
  

   bands 
  to 
  the 
  subjacent 
  and 
  superjacent 
  strata. 
  It 
  appears 
  to 
  me 
  

   that 
  such 
  bands 
  in 
  many 
  cases 
  immediately 
  overlie 
  or 
  are 
  directly 
  

   connected 
  with 
  beds 
  displaying 
  evidence 
  of 
  the 
  commencement 
  of 
  

   depression, 
  or 
  partial 
  elevation 
  of 
  deep-water 
  beds 
  accompanied 
  by 
  

   current-action. 
  For 
  example, 
  outside 
  Ireland, 
  in 
  the 
  South-east 
  of 
  

  

  1 
  ' 
  The 
  Genesis 
  of 
  the 
  Chalk,' 
  Proc. 
  Geol. 
  Assoc, 
  vol. 
  xiii. 
  (1894) 
  p. 
  233. 
  

  

  