﻿542 
  DE. 
  W. 
  FEASEE 
  HUME 
  ON 
  [Dec. 
  1 
  897, 
  

  

  varies 
  with 
  the 
  locality. 
  On 
  the 
  whole, 
  I 
  find 
  that, 
  in 
  ascending 
  

   the 
  bed, 
  it 
  becomes 
  more 
  and 
  more 
  compact, 
  by 
  the 
  predominance 
  of 
  

   the 
  calcareous 
  paste, 
  and 
  the 
  siliceous 
  and 
  chloride 
  elements 
  become 
  

   less 
  and 
  less 
  in 
  amount, 
  finally 
  passing 
  up 
  insensibly 
  into 
  the 
  con- 
  

   dition 
  of 
  a 
  white 
  compact 
  limestone.' 
  Apart 
  from 
  the 
  use 
  of 
  the 
  

   term 
  ' 
  chloritic 
  ' 
  instead 
  of 
  ' 
  glauconitic,' 
  the 
  above 
  description 
  

   accurately 
  states 
  the 
  character 
  of 
  this 
  interesting 
  set 
  of 
  beds. 
  

  

  The 
  Yellow 
  Sandstones 
  are 
  normally 
  of 
  a 
  brown 
  to 
  yellow 
  

   colour, 
  frequently 
  containing 
  well-marked 
  bands 
  of 
  chert. 
  Marly 
  

   layers 
  may 
  occur 
  throughout, 
  but 
  are 
  especially 
  developed 
  at 
  the 
  

   base. 
  

  

  Finally, 
  the 
  Glauconitic 
  Sands 
  are 
  of 
  a 
  deep 
  green 
  colour, 
  

   and 
  in 
  many 
  localities 
  mainly 
  consist 
  of 
  glauconitic 
  grains. 
  

  

  Tate 
  further 
  subdivided 
  the 
  lithological 
  divisions 
  into 
  zones 
  

   which 
  were 
  named 
  after 
  the 
  characteristic 
  fossils. 
  Thus 
  the 
  White 
  

   Limestone 
  became 
  the 
  zone 
  of 
  Ammonites 
  gollevillensis, 
  while 
  the 
  

   Chloritic 
  Chalk 
  included 
  a 
  Spongiarian 
  zone 
  and 
  that 
  of 
  Anancliytes 
  

   gibbas, 
  a 
  band 
  containing 
  the 
  latter 
  species 
  being 
  taken 
  as 
  the 
  base 
  

   of 
  the 
  Upper 
  Chalk 
  or 
  Senonian. 
  

  

  On 
  the 
  other 
  hand, 
  the 
  Chloritic 
  Sands 
  (including 
  the 
  two 
  zones 
  

   of 
  Exogyra 
  columba 
  and 
  Inoceramus 
  Crispi), 
  the 
  Yellow 
  Sandstones 
  

   (zone 
  of 
  Ostrea 
  carinata), 
  and 
  the 
  Glauconitic 
  Sands 
  (zone 
  of 
  Exogyra 
  

   conicd) 
  were 
  all 
  classed 
  as 
  members 
  of 
  the 
  Cenomanian. 
  The 
  general 
  

   conclusion, 
  therefore, 
  is 
  that 
  a 
  palseontological 
  hiatus 
  must 
  have 
  

   existed 
  between 
  the 
  Chloritic 
  Chalk 
  and 
  Chloritic 
  Sands 
  : 
  the 
  whole 
  

   of 
  the 
  Turonian, 
  and 
  a 
  good 
  part 
  of 
  the 
  Senonian 
  beds 
  being 
  un- 
  

   represented 
  in 
  the 
  series. 
  

  

  Barrois 
  re-examined 
  the 
  strata 
  in 
  the 
  light 
  of 
  his 
  researches 
  on 
  

   the 
  English 
  Cretaceous 
  zones, 
  and 
  came 
  to 
  the 
  conclusion 
  that 
  the 
  

   Tnronian, 
  or 
  Middle 
  Chalk, 
  was 
  clearly 
  represented 
  in 
  the 
  Irish 
  

   district, 
  certain 
  bands, 
  rich 
  in 
  Inoceramus-fmgments, 
  being 
  especially 
  

   characterized 
  by 
  Turonian 
  fossils. 
  These, 
  according 
  to 
  him, 
  showed 
  

   the 
  existence 
  of 
  the 
  higher 
  zones, 
  namely, 
  Holaster 
  planus 
  and 
  Tere- 
  

   bratnlina 
  gracilis, 
  that 
  of 
  Inoceramus 
  labiatus 
  being 
  unrepresented. 
  

   He 
  further 
  believed 
  all 
  the 
  Senonian 
  divisions 
  to 
  be 
  present, 
  whereas 
  

   Tate 
  placed 
  the 
  zone 
  of 
  Ananchytes 
  gibbus 
  on 
  a 
  level 
  with 
  that 
  of 
  

   Belemnitella 
  quadrata, 
  in 
  the 
  Upper 
  Senonian. 
  The 
  zones 
  of 
  

   Ostrea 
  carinata 
  and 
  Exogyra 
  conica 
  were 
  referred 
  by 
  him 
  to 
  the 
  

   Cenomanian. 
  

  

  Neither 
  of 
  the 
  two 
  authors 
  above 
  mentioned 
  have 
  made 
  any 
  

   reference 
  to 
  the 
  remarkable 
  conglomerates 
  which 
  form 
  the 
  base 
  of 
  

   the 
  White 
  Chalk 
  where 
  the 
  latter 
  rests 
  upon 
  beds 
  of 
  more 
  ancient 
  

   date, 
  such 
  as 
  the 
  Trias, 
  Carboniferous, 
  or 
  metamorphic 
  rocks 
  of 
  a 
  

   still 
  older 
  period 
  (mica-schists, 
  etc.). 
  These 
  beds 
  were 
  recognized 
  

   and 
  carefully 
  examined 
  by 
  Portlock. 
  1 
  He 
  also 
  divided 
  the 
  Cretaceous 
  

  

  1 
  'Report 
  on 
  Geol. 
  Londonderry, 
  etc./ 
  1843. 
  See 
  especially 
  pp. 
  115 
  & 
  749, 
  

   and 
  generally 
  pp. 
  90-140, 
  where 
  many 
  references 
  to 
  the 
  White 
  Chalk 
  and 
  its 
  

   subjacent 
  beds 
  will 
  be 
  found. 
  

  

  