﻿126 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  

  

  underlying 
  Portland 
  Limestone 
  corresponds 
  to 
  the 
  Trigonia- 
  

   bed 
  of 
  Swindon. 
  Hence 
  the 
  Purbeck 
  beds 
  of 
  Oxfordshire 
  

   and 
  Buckinghamshire 
  are 
  of 
  earlier 
  date 
  than 
  the 
  Portland 
  

   of 
  Swindon, 
  and 
  still 
  earlier 
  than 
  those 
  of 
  the 
  Isle 
  of 
  Pur- 
  

   beck, 
  and 
  were 
  formed 
  in 
  Portland 
  times. 
  

  

  10. 
  The 
  fossiliferous 
  Portland 
  Sand 
  becomes 
  much 
  diminished 
  

  

  in 
  importance, 
  but 
  continues 
  its 
  glauconitic 
  character, 
  to 
  the 
  

   north, 
  while 
  the 
  lowest 
  sands 
  with 
  their 
  rounded 
  masses 
  

   are 
  continued 
  to 
  Shotover 
  and 
  Thame 
  and 
  then 
  nearly 
  

   disappear. 
  

  

  11. 
  Thus 
  the 
  Portland 
  Sand 
  had 
  two 
  maxima 
  — 
  one 
  to 
  the 
  north 
  

  

  of 
  Tisbury, 
  and 
  one 
  to 
  the 
  south 
  ; 
  but 
  as 
  regards 
  the 
  Portland 
  

   Stone 
  the 
  oldest 
  beds 
  are 
  found 
  in 
  the 
  north, 
  and 
  as 
  we 
  go 
  

   south 
  later 
  and 
  later 
  deposits 
  are 
  successively 
  introduced 
  

   before 
  the 
  traces 
  of 
  freshwater 
  conditions 
  appear. 
  

  

  12. 
  These 
  were 
  the 
  final 
  result 
  of 
  the 
  gradual 
  elevation 
  in 
  all 
  

  

  cases, 
  and 
  were 
  not 
  of 
  the 
  same 
  age 
  throughout, 
  but 
  followed 
  

   immediately 
  on 
  the 
  period 
  of 
  the 
  beds 
  below 
  (loc. 
  cit. 
  

   pp. 
  221, 
  222). 
  

  

  Little 
  trace 
  of 
  a 
  Portlandian 
  episode 
  can 
  be 
  detected 
  at 
  Speeton 
  

   in 
  Yorkshire, 
  or 
  beneath 
  Sussex, 
  and 
  Mr. 
  Blake 
  believes 
  " 
  that 
  the 
  

   elevation 
  which 
  introduced 
  the 
  circumstances 
  capable 
  of 
  yielding 
  

   sandy 
  and 
  calcareous 
  deposits 
  took 
  place 
  sporadically. 
  So 
  far 
  as 
  

   our 
  knowledge 
  at 
  present 
  extends, 
  the 
  earliest 
  rise 
  took 
  place 
  along 
  

  

  the 
  main 
  axis 
  between 
  Boulogne 
  and 
  the 
  Mendips 
  Further 
  

  

  physical 
  changes 
  of 
  a 
  nature 
  unknown 
  to 
  us 
  brought 
  about 
  the 
  de- 
  

   nudation 
  of 
  some 
  sandy 
  rocks 
  and 
  developed 
  the 
  great 
  sandbanks 
  

   which 
  pass 
  from 
  Swindon 
  to 
  Shotover 
  and 
  die 
  away 
  to 
  the 
  north- 
  

   east, 
  and 
  which 
  diminish 
  from 
  St. 
  Alban's 
  Head 
  towards 
  Portland 
  

   and 
  Upway, 
  and 
  are 
  not 
  to 
  be 
  recognized 
  in 
  the 
  Boulogne 
  area." 
  

  

  The 
  question 
  of 
  the 
  removal 
  of 
  the 
  Portland 
  Sands 
  to 
  the 
  Kim- 
  

   meridge 
  Clay 
  is 
  commented 
  upon 
  ; 
  and 
  the 
  propriety 
  of 
  the 
  French 
  

   geologists 
  uniting 
  the 
  upper 
  part 
  of 
  the 
  Kimmeridge 
  Clay 
  with 
  the 
  

   Portland 
  sands, 
  and 
  calling 
  them 
  the 
  " 
  Middle 
  Portlandian," 
  is 
  

   clearly 
  stated. 
  Mr. 
  Blake 
  has 
  added 
  a 
  complete 
  table 
  of 
  Portlan- 
  

   dian 
  fossils, 
  adding 
  17 
  new 
  species, 
  and 
  introducing 
  8 
  continental 
  

   forms 
  (French) 
  as 
  new 
  to 
  Britain, 
  thus 
  increasing 
  our 
  Portlandian 
  

   fauna 
  by 
  25 
  additional 
  species. 
  I 
  have 
  reconstructed 
  the 
  table 
  so 
  

   as 
  to 
  read 
  uniformly 
  with 
  those 
  prepared 
  in 
  other 
  portions 
  of 
  my 
  

   address 
  for 
  this 
  year 
  and 
  the 
  year 
  1880-81 
  ; 
  for 
  the 
  names 
  of 
  the 
  

   species 
  vide 
  Mr. 
  Blake's 
  Table, 
  loc. 
  cit. 
  pp. 
  225-227. 
  

  

  