﻿VerriU 
  — 
  Notes 
  on 
  the 
  Geology 
  of 
  the 
  Bermudas. 
  321 
  

  

  10. 
  A 
  process 
  of 
  secondary 
  infiltration 
  of 
  the 
  rocks 
  with 
  

   solutions 
  of 
  calcium 
  bicarbonate 
  and 
  the 
  deposition 
  of 
  calcite, 
  

   thus 
  filling 
  the 
  pores 
  more 
  or 
  less 
  completely 
  and 
  hardening 
  

   the 
  rock 
  much 
  be 
  von 
  d 
  its 
  original 
  condition, 
  is 
  a 
  very 
  

   important 
  factor 
  in 
  Bermudian 
  geology 
  as 
  affecting 
  both 
  the 
  

   littoral 
  and 
  subrenal 
  erosion. 
  There 
  is 
  good 
  evidence 
  that 
  this 
  

   has 
  taken 
  place 
  extensively, 
  not 
  only 
  at 
  the 
  surface 
  but 
  at 
  a 
  

   considerable 
  and 
  variable 
  depth 
  below 
  the 
  surface 
  of 
  the 
  rocks, 
  

   at 
  levels 
  corresponding 
  to 
  the 
  variable 
  upper 
  limits 
  of 
  the 
  zone 
  

   of 
  aqueous 
  saturation, 
  where 
  the 
  evaporation 
  of 
  the 
  water 
  and 
  

   periodical 
  sinking 
  of 
  the 
  water 
  level 
  would 
  cause 
  such 
  a 
  deposit 
  

   to 
  form. 
  As 
  all 
  the 
  porous 
  rocks, 
  up 
  to 
  the 
  level 
  of 
  mid-tide, 
  

   are 
  saturated 
  with 
  sea 
  water, 
  on 
  which 
  the 
  layer 
  of 
  fresh 
  water 
  

   rests," 
  this 
  zone 
  of 
  calcification 
  would 
  always 
  be 
  higher 
  than 
  

   that 
  level 
  and 
  locally 
  might 
  be 
  many 
  feet 
  above 
  high-tide 
  leveL 
  

  

  11. 
  Probably 
  most 
  of 
  the 
  so-called 
  base-rock 
  has 
  been 
  formed 
  

   in 
  this 
  way, 
  by 
  the 
  calcification 
  of 
  ordinary 
  seolian 
  limestones. 
  f 
  

   Thus 
  a 
  " 
  base-rock 
  " 
  of 
  this 
  kind 
  would 
  naturally 
  be 
  most 
  often 
  

   formed 
  a 
  little 
  above 
  high-tide 
  level, 
  underlying 
  unconfonn- 
  

   ably 
  the 
  aeolian 
  limestones. 
  This 
  is 
  the 
  position 
  in 
  which 
  

   this 
  rock 
  generally 
  occurs, 
  but 
  it 
  is 
  also 
  found 
  at 
  various 
  other 
  

   levels, 
  as 
  might 
  be 
  expected, 
  and 
  it 
  is 
  often 
  lacking, 
  both 
  in 
  

   natural 
  shore-sections 
  and 
  in 
  artificial 
  ones4 
  Similar 
  calcifica- 
  

   tion 
  of 
  the 
  rock 
  may 
  occur 
  locally 
  at 
  or 
  near 
  the 
  surface. 
  

  

  Doubtless 
  similar 
  effects 
  producing 
  similar 
  results 
  have 
  

   occurred 
  at 
  various 
  levels 
  and 
  at 
  various 
  periods 
  during 
  the 
  

   former 
  changes 
  in 
  the 
  elevation 
  of 
  the 
  islands, 
  for 
  both 
  eleva- 
  

   tion 
  and 
  submergence 
  were 
  probably 
  intermittent, 
  with 
  long 
  

   periods 
  of 
  rest. 
  

  

  Rocks 
  exposed 
  to 
  the 
  surf 
  along 
  the 
  shores, 
  both 
  between 
  

   tides 
  and 
  high 
  up 
  on 
  the 
  cliffs, 
  become 
  deeply 
  pitted 
  and 
  honey 
  - 
  

  

  * 
  Shallow 
  wells 
  and 
  tanks 
  have 
  often 
  been 
  excavated 
  on 
  the 
  islands, 
  but 
  when 
  

   they 
  go 
  below 
  mid-tide-level 
  the 
  water 
  at 
  the 
  bottom 
  is 
  always 
  salt 
  or 
  brackish, 
  

   and 
  the 
  fresh 
  water, 
  which 
  floats 
  on 
  the 
  salt, 
  can 
  only 
  be 
  obtained 
  fit 
  for 
  use 
  at 
  

   certain 
  stages 
  of 
  the 
  tide. 
  

  

  fThe 
  ; 
  ' 
  base 
  rock' 
  1 
  sometimes 
  shows 
  distinct 
  ceolian 
  stratification, 
  though 
  it 
  is 
  

   more 
  commonly 
  nearly 
  homogeneous 
  and 
  without 
  stratificatiou 
  where 
  best 
  devel- 
  

   oped. 
  It 
  is 
  composed 
  of 
  shell-sand 
  like 
  the 
  ordinary 
  reolian 
  rocks. 
  I 
  could 
  not 
  

   find 
  evidence 
  that 
  the 
  so-called 
  base 
  rock 
  represents 
  a 
  distinct 
  period 
  as 
  explained 
  

   in 
  sections 
  4 
  and 
  5. 
  Mr. 
  A. 
  Agassiz 
  also 
  failed 
  to 
  recognize 
  them 
  as 
  a 
  distinct 
  

   formation, 
  but 
  Professors 
  Rice. 
  Tarr. 
  and 
  Stevenson 
  all 
  considered 
  them 
  a 
  distinct 
  

   deposit 
  of 
  earlier 
  date 
  than 
  the 
  ordinary 
  seolian 
  limestones, 
  because 
  they 
  appear 
  

   in 
  some 
  cases 
  to 
  underlie 
  the 
  latter. 
  But 
  if 
  the 
  above 
  view 
  of 
  their 
  origin 
  be 
  cor- 
  

   rect, 
  this 
  does 
  not 
  indicate 
  a 
  distinct 
  formation 
  nor 
  earlier 
  period. 
  

  

  \ 
  The 
  rock 
  found 
  beneath 
  the 
  peat 
  bog 
  at 
  Ireland 
  Island 
  at 
  the 
  depth 
  of 
  50 
  feet 
  

   has 
  been 
  described 
  as 
  " 
  the 
  ordinary 
  base 
  rock 
  " 
  with 
  irregular 
  upper 
  surface, 
  

   and 
  also 
  as 
  an 
  ceolian 
  limestone. 
  In 
  either 
  case 
  it 
  was 
  doubtless 
  consolidated 
  

   above 
  sea 
  level 
  by 
  infiltration. 
  The 
  more 
  recent 
  loose 
  deposits 
  (about 
  30 
  feet 
  

   thick) 
  above 
  the 
  peat 
  were 
  not 
  consolidated 
  and 
  consisted 
  of 
  shell-sand, 
  broken 
  

   shells 
  and 
  massive 
  corals 
  and 
  pebbles. 
  Such 
  materials 
  at 
  Bermuda 
  do 
  not 
  seem 
  

   able 
  to 
  consolidate 
  into 
  limestone 
  beneath 
  the 
  sea. 
  

  

  