﻿320 
  Yerrill 
  — 
  Notes 
  on 
  the 
  Geology 
  of 
  the 
  Bermudas. 
  

  

  tion 
  and 
  subsidence 
  in 
  which 
  the 
  elevation 
  was 
  intermediate 
  

   between 
  that 
  of 
  the 
  Greater 
  Bermuda 
  and 
  the 
  present, 
  or 
  when 
  

   the 
  land 
  stood 
  from 
  30 
  to 
  60 
  feet 
  higher 
  than 
  now, 
  thus 
  con- 
  

   necting 
  the 
  extensive 
  bays 
  and 
  sounds 
  into 
  great 
  sand-flats, 
  

   more 
  or 
  less 
  extensively 
  covered 
  by 
  the 
  tides 
  at 
  high 
  water, 
  

   and 
  bordered 
  by 
  broad 
  sand 
  beaches 
  laid 
  bare 
  at 
  low 
  water 
  

   from 
  which 
  vast 
  quantities 
  of 
  sand 
  could 
  be 
  taken 
  and 
  carried 
  

   inland 
  by 
  the 
  winds. 
  At 
  present 
  the 
  sand-beaches 
  are 
  all 
  of 
  

   small 
  extent. 
  It 
  is 
  probable 
  that 
  the 
  higher 
  hills 
  of 
  the 
  pres- 
  

   ent 
  land 
  represent 
  the 
  older 
  sand-dunes 
  formed 
  during 
  the 
  

   elevation 
  of 
  Greater 
  Bermuda.* 
  

  

  8. 
  Erosion 
  has 
  occurred 
  on 
  a 
  grand 
  scale 
  since 
  the 
  sub- 
  

   mergence 
  took 
  place, 
  cutting 
  away 
  the 
  shore 
  cliffs 
  to 
  a 
  very 
  

   great 
  extent, 
  converting 
  many 
  of 
  the 
  outer 
  islands 
  into 
  mere 
  

   platforms 
  of 
  rock, 
  either 
  a 
  little 
  below 
  the 
  level 
  of 
  the 
  sea 
  at 
  

   low 
  tide 
  or 
  just 
  rising 
  above 
  it, 
  and 
  also 
  occasionally 
  leaving 
  

   detached 
  pinnacles 
  of 
  harder 
  rock 
  on 
  the 
  outer 
  ledges 
  and 
  

   reefs, 
  of 
  which 
  the 
  most 
  remarkable 
  are 
  the 
  North 
  Rocks 
  (fig. 
  

   11) 
  which 
  stand 
  on 
  a 
  large 
  flat 
  submerged 
  reef 
  about 
  8 
  miles 
  

   from 
  the 
  islands. 
  They 
  are 
  clearly 
  composed 
  of 
  seolian 
  lime- 
  

   stone, 
  rendered 
  hard 
  by 
  infiltrations 
  of 
  calcite. 
  

  

  9. 
  The 
  rate 
  of 
  the 
  erosion 
  by 
  the 
  sea 
  has 
  been 
  greatly 
  exag- 
  

   gerated 
  by 
  most 
  writers. 
  Data 
  obtained 
  by 
  me 
  indicate 
  that 
  it 
  

   must 
  have 
  taken 
  at 
  least 
  25,000 
  to 
  30,000 
  years 
  to 
  accomplish 
  

   the 
  erosion 
  of 
  the 
  high 
  cliffs 
  facing 
  on 
  Hamilton 
  Sound, 
  which 
  

   is 
  nearly 
  land-locked. 
  The 
  data 
  hitherto 
  obtained 
  applies 
  

   better 
  to 
  the 
  erosion 
  of 
  the 
  cliffs 
  of 
  Hamilton 
  Sound 
  than 
  to 
  

   that 
  of 
  the 
  outer 
  cliffs. 
  So 
  far, 
  we 
  have 
  not 
  been 
  able 
  to 
  get 
  

   any 
  reliable 
  data 
  for 
  estimating 
  the 
  amount 
  and 
  rapidity 
  of 
  the 
  

   erosion 
  of 
  the 
  exposed 
  cliffs, 
  especially 
  of 
  those 
  on 
  the 
  south 
  

   shore 
  where 
  the 
  erosion 
  is 
  most 
  rapid 
  and 
  extensive. 
  A 
  care- 
  

   ful 
  comparison 
  that 
  I 
  have 
  made 
  between 
  recent 
  maps 
  and 
  a 
  

   good 
  map 
  published 
  274 
  years 
  ago 
  shows 
  very 
  little 
  change 
  in 
  

   the 
  size 
  or 
  outlines, 
  of 
  the 
  islands, 
  bays, 
  and 
  harbors 
  since 
  that 
  

   time.f 
  

  

  * 
  A 
  fuller 
  discussion 
  and 
  more 
  illustrations 
  of 
  this 
  and 
  other 
  points 
  of 
  Bermu- 
  

   dian 
  Geology 
  will 
  be 
  given 
  in 
  a 
  more 
  extensive 
  paper, 
  to 
  be 
  published 
  in 
  the 
  

   Transactions 
  of 
  the 
  Connecticut 
  Acad, 
  of 
  Sciences, 
  Vol. 
  XI. 
  

  

  \ 
  The 
  map 
  particularly 
  referred 
  to 
  was 
  made 
  by 
  Richard 
  Norwood, 
  before 
  

   1622. 
  " 
  A 
  mapp 
  of 
  the 
  Sommer 
  Islands, 
  once 
  called 
  the 
  Bermudas," 
  London, 
  

   1626. 
  Reprinted 
  from 
  an 
  original 
  engraving 
  in 
  the 
  British 
  Museum, 
  by 
  Governor 
  

   Lefroy 
  in 
  " 
  Memorials 
  of 
  the 
  Discovery 
  and 
  early 
  Settlement 
  of 
  the 
  Bermudas 
  or 
  

   Somer's 
  Islands," 
  London, 
  lSIT 
  (end 
  of 
  vol. 
  I). 
  A 
  much 
  less 
  complete 
  edition 
  of 
  

   this 
  or 
  an 
  earlier 
  map 
  was 
  published 
  in 
  1624, 
  in 
  Capt. 
  John 
  Smith's 
  "General 
  

   History 
  of 
  Virginia, 
  New 
  England, 
  and 
  the 
  Summer 
  lis." 
  

  

  A 
  later 
  survey 
  and 
  map 
  by 
  Norwood, 
  completed 
  in 
  1663, 
  has 
  also 
  been 
  reprinted 
  

   by 
  Gov. 
  Lefroy, 
  in 
  the 
  work 
  cited, 
  p. 
  644, 
  but 
  the 
  shore 
  lines 
  are 
  much 
  coarser 
  

   and 
  less 
  accurate 
  in 
  the 
  latter, 
  which 
  was 
  made 
  mainly 
  with 
  reference 
  to 
  the 
  

   transfers 
  of 
  land 
  and 
  the 
  boundaries 
  of 
  estates. 
  See 
  additional 
  discussion 
  of 
  the 
  

   maps, 
  p. 
  324. 
  

  

  