﻿ANNIVERSARY 
  ADDRESS 
  OF 
  THE 
  PRESIDENT. 
  1 
  25 
  

  

  Buckingham 
  shire 
  and 
  the 
  Trigonia-beds 
  of 
  Swindon 
  and 
  Bourton, 
  

   and 
  peculiar 
  to 
  these 
  or 
  most 
  common 
  in 
  them. 
  They 
  are 
  : 
  — 
  

  

  Ammonites 
  pectinatus. 
  Pleuromya 
  tellina. 
  

  

  Natica 
  elegans. 
  Thracia 
  tenera. 
  

  

  Trigonia 
  Voltzii. 
  Mytilus 
  unguiculatus. 
  

  

  Cyprina 
  elongata. 
  boloniensis. 
  

  

  Cypricardia 
  costifera. 
  Echinobrissus 
  Brodiei. 
  

   Anisocardia 
  pulchella. 
  

  

  The 
  Natica, 
  Cyprina, 
  Cypricardia, 
  Anisocardia, 
  Pleuromya, 
  and 
  

   Echinobrissus 
  occur 
  in 
  the 
  creamy 
  limestones, 
  which 
  thus 
  range 
  no 
  

   higher 
  than 
  the 
  beds 
  at 
  Swindon. 
  Mr. 
  Blake 
  therefore 
  regards 
  " 
  the 
  

   whole 
  of 
  the 
  limestones 
  of 
  Buckinghamshire 
  as 
  an 
  expansion 
  of 
  the 
  

   Trigonia-beds 
  of 
  Swindon, 
  except 
  that 
  the 
  brashy 
  beds 
  at 
  the 
  top 
  

   correspond 
  to 
  part 
  of 
  the 
  ' 
  basal 
  sands 
  ' 
  of 
  the 
  latter 
  place, 
  but 
  not 
  

   to 
  the 
  whole." 
  

  

  The 
  author 
  then 
  summarizes 
  the 
  contents 
  of 
  his 
  paper, 
  and 
  re- 
  

   capitulates 
  the 
  facts 
  arrived 
  at, 
  which 
  may 
  be 
  stated 
  as 
  follows 
  : 
  — 
  

  

  1. 
  In 
  all 
  the 
  sections 
  near 
  the 
  coast 
  the 
  Purbeck 
  beds 
  are 
  sepa- 
  

  

  rated 
  from 
  the 
  Portland 
  by 
  a 
  line 
  of 
  clay. 
  

  

  2. 
  The 
  uppermost 
  bed 
  of 
  the 
  Purbeck 
  is 
  not 
  always 
  the 
  same, 
  

  

  and 
  the 
  line 
  of 
  junction, 
  though 
  not 
  eroded, 
  is 
  "irregular." 
  

  

  3. 
  The 
  Portland 
  series 
  (reading 
  downwards) 
  shows 
  first 
  the 
  

  

  "Whit 
  bed" 
  and 
  "Boach" 
  characterized 
  by 
  particular 
  

   fossils, 
  and 
  especially 
  by 
  Ammonites 
  giganteus, 
  and 
  locally 
  

   unconformable 
  to 
  the 
  bed 
  below. 
  

  

  4. 
  The 
  flinty 
  series 
  is 
  divisible 
  into 
  several 
  parts, 
  very 
  fossiliferous 
  

  

  at 
  the 
  base, 
  arid 
  characterized 
  by 
  Ammonites 
  boloniensis. 
  

   This 
  is 
  thickest 
  at 
  St. 
  Alban's 
  Head, 
  and 
  becomes 
  chalky 
  at 
  

   Up 
  way. 
  

  

  5. 
  The 
  Portland 
  Sands 
  contain 
  a 
  variety 
  of 
  beds 
  (clays, 
  cement- 
  

  

  stones, 
  and 
  oyster-beds), 
  and 
  have 
  a 
  fauna 
  distinct 
  from 
  

   that 
  of 
  the 
  limestones 
  above 
  ; 
  but 
  these 
  characters 
  are 
  not 
  

   constant. 
  

  

  6. 
  "In 
  the 
  Yale 
  of 
  Wardour 
  the 
  Purbeck 
  is 
  separated 
  from 
  the 
  

  

  Portland 
  by 
  a 
  band 
  of 
  clay, 
  and 
  the 
  succession 
  is 
  very 
  

   similar. 
  Below 
  the 
  Limestones 
  the 
  true 
  Portland 
  Sand 
  is 
  

   very 
  thin 
  and 
  brown." 
  

  

  7. 
  At 
  Swindon 
  the 
  relations 
  of 
  the 
  Purbeck 
  to 
  the 
  Portland 
  are 
  

  

  remarkable 
  ; 
  the 
  Portland 
  is 
  carved 
  out 
  in 
  hollows 
  which 
  

   contain 
  rolled 
  blocks 
  of 
  it, 
  evidencing 
  a 
  land 
  surface 
  and 
  rapid 
  

   changes. 
  This 
  erosion 
  may 
  have 
  taken 
  place 
  in 
  Portland 
  

   times, 
  as 
  the 
  uppermost 
  part 
  of 
  the 
  Portland 
  beds 
  here 
  

   corresponds 
  only 
  to 
  the 
  top 
  of 
  the 
  Tisbury 
  Freestone. 
  

  

  8. 
  The 
  Portland 
  sands 
  are 
  found 
  at 
  Swindon 
  below 
  the 
  Trigonia- 
  

  

  beds, 
  and 
  occur 
  in 
  the 
  form 
  of 
  extremely 
  fossiliferous 
  glauco- 
  

   nitic 
  sandstones 
  or 
  shell 
  masses. 
  They 
  contain 
  a 
  well-marked 
  

   and 
  almost 
  restricted 
  fauna. 
  

  

  9. 
  The 
  districts 
  of 
  Oxfordshire 
  and 
  Buckinghamshire 
  are 
  formed 
  

  

  on 
  the 
  same 
  model. 
  The 
  Purbeck 
  beds 
  of 
  Bucks 
  lie 
  

   uniformly 
  on 
  the 
  Portland 
  rocks 
  as 
  in 
  the 
  south 
  ; 
  but 
  the 
  

  

  