﻿600 
  DR. 
  W. 
  FEASER 
  HUME 
  ON 
  [Dec. 
  1 
  89 
  7, 
  

  

  the 
  palseontologieal 
  evidence 
  points 
  to 
  the 
  conclusion 
  that 
  during 
  the 
  

   deposition 
  of 
  the 
  Upper 
  Greensaud 
  the 
  English 
  and 
  Irish 
  Cretaceous 
  

   seas 
  formed 
  part 
  of 
  the 
  same 
  geographical 
  province. 
  

  

  2. 
  A 
  second 
  difficulty 
  arises 
  in 
  regard 
  to 
  the 
  Chloritic 
  Sands 
  and 
  

   their 
  divisions, 
  the 
  zones 
  of 
  Exogyra 
  columba 
  and 
  Inoceramus 
  Crispi. 
  

   Why 
  should 
  the 
  beds 
  containing 
  the 
  former 
  be 
  developed 
  on 
  so 
  ex- 
  

   tensive 
  a 
  scale 
  south 
  of 
  Belfast, 
  yet 
  scarcely 
  be 
  known 
  north 
  of 
  that 
  

   city 
  ; 
  and 
  for 
  what 
  reason 
  does 
  the 
  precise 
  opposite 
  hold 
  good 
  for 
  the 
  

   strata 
  containing 
  Inoceramns-fragments 
  and 
  JSpondylus 
  spinosus 
  ? 
  

  

  The 
  following 
  suggestion 
  appears 
  to 
  offer 
  the 
  best 
  solution 
  of 
  the 
  

   enigma. 
  The 
  detrital 
  deposits 
  will 
  be, 
  speaking 
  in 
  general 
  terms, 
  

   thicker 
  nearer 
  a 
  continental 
  shore-line 
  than 
  they 
  would 
  be 
  farther 
  

   out 
  at 
  sea. 
  Eeasons 
  have 
  already 
  been 
  given 
  for 
  believing 
  that 
  the 
  

   Central 
  Division 
  was 
  closer 
  to 
  land 
  than 
  the 
  Eastern, 
  and 
  we 
  have 
  

   seen 
  that 
  at 
  Colin 
  Glen 
  the 
  beds 
  (largely 
  composed 
  of 
  land-derived 
  

   materials) 
  below 
  the 
  mulatto-stone 
  are 
  60 
  feet 
  thick. 
  In 
  the 
  

   Eastern 
  area 
  the 
  corresponding 
  beds 
  do 
  not, 
  at 
  their 
  maximum, 
  

   exceed 
  30 
  feet. 
  If 
  elevation 
  took 
  place, 
  the 
  strata 
  nearest 
  the 
  land 
  

   would 
  first 
  commence 
  to 
  be 
  denuded, 
  but, 
  should 
  the 
  geocratic 
  

   tendency 
  not 
  be 
  prolonged, 
  being 
  of 
  considerable 
  thickness, 
  a 
  portion 
  

   of 
  the 
  older 
  beds 
  would 
  still 
  remain 
  unaffected 
  by 
  denudation. 
  On 
  

   the 
  other 
  hand, 
  the 
  thinner 
  strata 
  formed 
  in 
  deeper 
  water 
  would 
  be 
  

   less 
  liable 
  to 
  denudation, 
  and 
  on 
  depression 
  recommencing, 
  organic 
  

   calcareous 
  deposits 
  would 
  commence 
  to 
  form 
  earlier 
  here 
  than 
  in 
  the 
  

   littoral 
  regions. 
  

  

  Our 
  explanation, 
  then, 
  is 
  this 
  : 
  — 
  The 
  strata 
  of 
  Upper 
  Greensand, 
  

   Cenomanian, 
  and 
  Turonian 
  age 
  in 
  Colin 
  Glen, 
  etc., 
  were 
  laid 
  

   down 
  nearer 
  shore, 
  and 
  were 
  in 
  consequence 
  thicker 
  than 
  the 
  

   corresponding 
  beds 
  in 
  the 
  Eastern 
  Division. 
  When 
  elevation 
  

   ensued, 
  the 
  Central 
  Division 
  was 
  first 
  affected 
  by 
  denudation, 
  

   and 
  any 
  Turonian 
  or 
  Upper 
  Cenomanian 
  strata 
  that 
  had 
  been 
  

   formed 
  were 
  removed. 
  On 
  the 
  other 
  hand, 
  in 
  the 
  Eastern 
  Division, 
  

   the 
  hydrocratic 
  movements 
  of 
  the 
  beginning 
  of 
  the 
  Upper 
  Chalk 
  

   period 
  resulted 
  in 
  the 
  formation 
  of 
  a 
  series 
  of 
  strata 
  of 
  organic 
  

   origin, 
  which 
  are 
  practically 
  unrepresented 
  farther 
  south-west. 
  As 
  

   a 
  consequence, 
  the 
  unconformity 
  in 
  the 
  Central 
  Division 
  is 
  at 
  the 
  

   summit, 
  in 
  the 
  Eastern 
  near 
  the 
  base, 
  of 
  the 
  Chloritic 
  Sands 
  : 
  the 
  

   greensands 
  included 
  under 
  this 
  name 
  being, 
  in 
  the 
  two 
  areas, 
  of 
  

   different 
  age, 
  and, 
  when 
  carefully 
  examined, 
  of 
  different 
  characters. 
  

  

  3. 
  In 
  ' 
  The 
  Genesis 
  of 
  the 
  Chalk 
  ' 
  ] 
  the 
  present 
  writer 
  has 
  main- 
  

   tained 
  that 
  the 
  zones 
  of 
  the 
  English 
  Chalk 
  have 
  been 
  produced 
  

   during 
  the 
  course 
  of 
  three 
  great 
  phases 
  of 
  movement, 
  the 
  first 
  of 
  

   submergence, 
  lasting 
  from 
  the 
  Upper 
  Greensand 
  to 
  Terebratulina 
  

   gracilis-times 
  (Middle 
  Chalk); 
  the 
  second, 
  of 
  partial 
  elevation, 
  the 
  

   most 
  visible 
  result 
  of 
  which 
  is 
  the 
  Chalk 
  Rock 
  ; 
  and 
  thirdly, 
  after 
  

   the 
  formation 
  of 
  this 
  prominent 
  lithological 
  feature, 
  a 
  further 
  

   period 
  of 
  submergence, 
  far 
  exceeding 
  in 
  magnitude 
  the 
  earlier 
  

  

  1 
  Proc. 
  Geol. 
  Assoc, 
  vol. 
  xiii. 
  (1894) 
  pp. 
  211-246. 
  

  

  