﻿584 
  DE. 
  W. 
  ERASEE 
  HUME 
  ON 
  [Dec. 
  1897, 
  

  

  shining 
  flakes 
  of 
  muscovite, 
  one 
  fragment 
  of 
  black 
  tourmaline 
  (schorl), 
  

   and 
  a 
  wine-yellow 
  rutile, 
  exhibiting 
  knee-shaped 
  twinning. 
  

   Compared 
  with 
  previous 
  experiments, 
  we 
  notice 
  here 
  : 
  — 
  

  

  1. 
  The 
  abundant 
  evidence 
  of 
  silicification. 
  

  

  2. 
  The 
  reduction 
  in 
  size 
  of 
  the 
  sponge-spicules. 
  

  

  Chalk, 
  18 
  feet 
  above 
  the 
  Conglomerate. 
  

   (No. 
  8 
  in 
  Table 
  II.) 
  

  

  After 
  solution 
  in 
  acid, 
  80*84 
  grammes 
  yielded 
  *922 
  gramme 
  of 
  

   residue 
  =1 
  '14°/. 
  

  

  The 
  analysis 
  is 
  therefore 
  as 
  follows 
  : 
  — 
  

  

  Carbonate 
  of 
  lime 
  98-86% 
  

  

  Clay, 
  etc 
  = 
  -840 
  gr. 
  = 
  1-039% 
  

  

  Heavy 
  residue 
  = 
  -082 
  „ 
  = 
  -101% 
  

  

  100 
  

  

  Of 
  the 
  latter 
  *0225 
  gramme 
  exceeding 
  *5 
  mm. 
  in 
  diameter 
  consists 
  

   almost 
  exclusively 
  of 
  the 
  thin 
  siliceous 
  fibrous 
  films 
  previously 
  

   described, 
  one 
  or 
  two 
  quartz-grains, 
  numerous 
  rods 
  and 
  masses 
  

   of 
  limonite, 
  extremely 
  porous, 
  and 
  seen 
  to 
  be 
  made 
  up 
  of 
  minute 
  

   rounded 
  grains. 
  Some 
  of 
  these, 
  when 
  broken 
  open, 
  are 
  seen 
  to 
  

   possess 
  a 
  distinct 
  labyrinthic 
  structure, 
  and 
  in 
  a 
  few 
  instances 
  

   fine 
  fibres 
  project 
  across 
  the 
  hollow 
  cavities. 
  Silicified 
  foraminifera 
  

   (one 
  a 
  much 
  altered 
  Ammodiscus), 
  and 
  ostracoda 
  such 
  as 
  Paracypris, 
  

   are 
  sparsely 
  distributed. 
  

  

  In 
  the 
  finer 
  residue 
  the 
  limonitic 
  rods 
  are 
  very 
  abundant, 
  together 
  

   with 
  minute 
  glauconitic 
  rods, 
  the 
  internal 
  casts 
  of 
  sponge-spicules, 
  

   and 
  numerous 
  rounded 
  spheres 
  or 
  complete 
  casts 
  of 
  foraminifera 
  

   (especially 
  of 
  Eotaline 
  and 
  Globigerinoid 
  types), 
  in 
  which 
  each 
  

   individual 
  chamber 
  is 
  still 
  bound 
  together 
  by 
  a 
  stoloniferous 
  

   connexion. 
  

  

  The 
  characteristic 
  features 
  of 
  this 
  residue 
  are 
  : 
  — 
  

  

  1. 
  The 
  abundance 
  of 
  limonitic 
  rods. 
  

  

  2. 
  The 
  great 
  rarity 
  of 
  quartz 
  and 
  other 
  detrital 
  minerals. 
  

  

  This 
  series 
  gives 
  a 
  very 
  complete 
  account 
  of 
  the 
  successive 
  

   changes 
  in 
  the 
  history 
  of 
  the 
  Peninsular 
  Division. 
  The 
  con- 
  

   glomerate 
  appears 
  to 
  represent 
  a 
  period 
  of 
  maximum 
  denudation 
  ; 
  

   but, 
  subsequent 
  to 
  its 
  formation, 
  the 
  evidence 
  points 
  to 
  a 
  gradual 
  

   and 
  continuous 
  deepening. 
  This 
  is 
  marked 
  by 
  : 
  — 
  

  

  (a) 
  The 
  gradual 
  diminution 
  in 
  the 
  size 
  of 
  the 
  quartz-grains. 
  

  

  (b) 
  The 
  reduction 
  in 
  the 
  number 
  and 
  size 
  of 
  the 
  heavy 
  minerals. 
  

  

  (c) 
  The 
  steady 
  increase 
  in 
  the 
  percentage 
  of 
  calcareous 
  con- 
  

   stituents. 
  

  

  (d) 
  The 
  reduction 
  in 
  the 
  size 
  of 
  the 
  spicular 
  casts. 
  

  

  (e) 
  The 
  diminution 
  in 
  the 
  size 
  of 
  the 
  foraminiferal 
  casts. 
  

  

  (/) 
  The 
  increase 
  in 
  limonitic 
  materials, 
  in 
  this 
  respect 
  agreeing 
  

   with 
  the 
  deeper-water 
  chalks 
  of 
  the 
  South-east 
  of 
  England. 
  

  

  