﻿646 
  ME. 
  J. 
  W. 
  GEEGOEY 
  OK 
  - 
  CYSTECHTXrS 
  CEASSTJS 
  

  

  In 
  the 
  case 
  of 
  at 
  least 
  the 
  two 
  Nucidce 
  the 
  evidence 
  would 
  be 
  quite 
  as 
  

   strong 
  in 
  support 
  of 
  their 
  Pliocene 
  age. 
  Mr. 
  Jukes-Browne 
  and 
  

   Prof. 
  Harrison 
  do 
  not 
  definitely 
  accept 
  Eorbes's 
  conclusion, 
  and 
  only 
  

   speak 
  * 
  of 
  the 
  beds 
  as 
  early 
  Tertiary 
  ; 
  but 
  the 
  evidence 
  of 
  the 
  two 
  

   species 
  of 
  Nucula, 
  whatever 
  it 
  is 
  worth, 
  would 
  make 
  the 
  beds 
  later 
  

   rather 
  than 
  earlier. 
  

  

  The 
  Radiol 
  arian 
  deposits 
  include 
  a 
  somewhat 
  variable 
  series 
  

   of 
  marls, 
  chalk, 
  and 
  ooze, 
  which 
  sometimes 
  amounts 
  to 
  about 
  

   2000 
  feet 
  in 
  thickness. 
  They 
  occur 
  in 
  many 
  parts 
  of 
  the 
  island, 
  

   and 
  rise 
  at 
  Hillaby 
  Mt. 
  to 
  a 
  height 
  of 
  about 
  1145 
  feet. 
  According 
  

   to 
  Sir 
  B. 
  Schomburgk 
  they 
  are 
  interstratified 
  between 
  beds 
  of 
  the 
  

   Scotland 
  formation 
  and 
  are 
  accordingly 
  of 
  the 
  same 
  age, 
  a 
  conclusion 
  

   hitherto 
  almost 
  universally 
  accepted. 
  We 
  now 
  learn, 
  however, 
  from 
  

   the 
  letters 
  of 
  Mr. 
  Jukes-Browne 
  and 
  Prof. 
  Harrison 
  already 
  quoted, 
  

   that 
  the 
  formations 
  are 
  quite 
  distinct, 
  and 
  that 
  the 
  Eadiolarian 
  de- 
  

   posits 
  rest 
  unconformably 
  on 
  the 
  Scotland 
  rocks, 
  between 
  the 
  latter 
  

   and 
  the 
  Coralline 
  limestone. 
  

  

  The 
  Coralline 
  limestone 
  is 
  the 
  most 
  recent 
  of 
  the 
  three 
  divisions, 
  

   and 
  extends 
  over 
  nearly 
  six 
  sevenths 
  of 
  the 
  island, 
  though 
  it 
  appar- 
  

   ently 
  does 
  not 
  exceed 
  from 
  150 
  to 
  200 
  feet 
  in 
  thickness 
  ; 
  the 
  lime- 
  

   stone 
  contains 
  a 
  good 
  many 
  shells, 
  Echinoderm 
  spines, 
  &c, 
  of 
  which 
  

   Schomburgk 
  publishes 
  f 
  a 
  list 
  of 
  59 
  species 
  ; 
  there 
  is 
  also 
  a 
  collection 
  

   in 
  the 
  Society's 
  Museum 
  ; 
  the 
  fossils 
  are 
  all 
  of 
  living 
  species, 
  and 
  there 
  

   can 
  be 
  no 
  doubt 
  of 
  the 
  Pleistocene 
  age 
  of 
  the 
  rock. 
  

  

  The 
  specimen 
  of 
  Cystechinus 
  crassus 
  was 
  obtained 
  on 
  the 
  Haynes- 
  

   field 
  Estate, 
  at 
  a 
  depth 
  of 
  166 
  feet 
  below 
  the 
  surface. 
  The 
  estate 
  is 
  

   situated 
  on 
  the 
  Coralline 
  limestone, 
  and 
  the 
  house 
  is 
  at 
  an 
  elevation 
  

   of 
  707 
  feet 
  above 
  the 
  sea. 
  The 
  Coralline 
  limestone 
  in 
  this 
  part 
  of 
  

   the 
  island 
  is 
  from 
  150 
  to 
  200 
  feet 
  in 
  thickness, 
  and 
  the 
  wells, 
  Mr. 
  

   Jukes-Browne 
  informs 
  me, 
  rarely 
  penetrate 
  through 
  the 
  limestone, 
  

   as 
  they 
  usually 
  find 
  water 
  near 
  its 
  base. 
  The 
  fossil 
  may, 
  however, 
  

   have 
  been 
  derived 
  from 
  a 
  well 
  deeper 
  than 
  usual, 
  or 
  from 
  a 
  boring, 
  

   and 
  thus 
  have 
  been 
  obtained 
  from 
  the 
  underlying 
  Eadiolarian 
  marl. 
  

   That 
  it 
  did 
  come 
  from 
  the 
  Eadiolarian 
  marl, 
  is 
  clearly 
  proved 
  by 
  the 
  

   matrix 
  ; 
  and 
  though 
  it 
  is 
  very 
  unlike 
  the 
  white 
  Barbados 
  chalk, 
  

   which 
  is 
  the 
  commonest 
  variety 
  in 
  collections, 
  it 
  agrees 
  very 
  closely 
  

   with 
  a 
  specimen 
  in 
  the 
  Society's 
  Museum 
  (Barbados 
  coll. 
  M 
  S. 
  jSTo. 
  12). 
  

   By 
  washing 
  the 
  matrix 
  an 
  abundance 
  of 
  Eadiolaria 
  of 
  the 
  typical 
  

   form 
  of 
  the 
  deposits 
  can 
  be 
  obtained, 
  though 
  not 
  so 
  perfect 
  as 
  those 
  

   from 
  the 
  white 
  chalk 
  ; 
  this 
  suggested 
  the 
  possibility 
  of 
  the 
  rock 
  

   being 
  composed 
  of 
  materials 
  accumulated 
  by 
  denudation 
  of 
  the 
  Eadio- 
  

   larian 
  ooze, 
  and 
  thus 
  being 
  of 
  the 
  age 
  of 
  the 
  Coralline 
  limestone. 
  A 
  

   couple 
  of 
  thin 
  sections 
  have 
  been 
  prepared 
  to 
  test 
  this 
  point, 
  and 
  they 
  

   quite 
  set 
  the 
  question 
  at 
  rest; 
  there 
  is 
  no 
  trace 
  of 
  any 
  coral 
  matter, 
  

   and 
  the 
  clay 
  is 
  seen 
  to 
  be 
  charged 
  with 
  Eadiolarian 
  tests, 
  spicules 
  

   and 
  fragments, 
  spicules 
  of 
  Actinolithus, 
  Geodites, 
  &c, 
  scattered 
  

   through 
  a 
  fine 
  argillaceous 
  matrix. 
  Dr. 
  Hinde 
  has 
  kindly 
  examined 
  

  

  * 
  A. 
  J. 
  Jukes-Browne 
  and 
  J. 
  B. 
  Harrison, 
  " 
  Tertiary 
  Chalk 
  in 
  Barbados," 
  

   Nature, 
  vol. 
  xxxix. 
  25th 
  April, 
  1889, 
  p. 
  607. 
  

   t 
  Schomburgk, 
  op. 
  cit. 
  pp. 
  562-5. 
  

  

  