﻿114 
  Agassiz 
  — 
  Explorations 
  of 
  the 
  " 
  Albatross." 
  

  

  When 
  the 
  material 
  is 
  not, 
  from 
  local 
  causes, 
  very 
  abundant, 
  or 
  

   is 
  washed 
  out 
  over 
  the 
  flats, 
  there 
  are 
  fewer 
  islands, 
  and 
  often 
  

   these 
  are 
  but 
  mere 
  islets 
  or 
  bars 
  for 
  long 
  reaches 
  of 
  shore, 
  

   forming 
  the 
  characteristic 
  weather 
  faces 
  of 
  many 
  of 
  the 
  lagoons. 
  

  

  Many 
  of 
  the 
  lagoons 
  are 
  filled 
  with 
  shoals 
  or 
  ledges 
  awash 
  

   or 
  a 
  few 
  feet 
  above 
  the 
  sea 
  level. 
  These 
  shoals 
  are 
  parts 
  of 
  

   the 
  old 
  ledge 
  which 
  have 
  not 
  as 
  yet 
  been 
  eroded, 
  and 
  the 
  dis- 
  

   integration 
  of 
  which 
  has 
  gone 
  far 
  to 
  supply 
  the 
  material 
  for 
  

   the 
  land 
  of 
  the 
  outer 
  rims 
  of 
  the 
  atolls. 
  In 
  Fakarava 
  there 
  

   were 
  no 
  less 
  than 
  36 
  islands 
  and 
  islets 
  and 
  ledges, 
  parts 
  of 
  a 
  

   former 
  great 
  flat, 
  now 
  broken 
  up, 
  existing 
  parallel 
  to 
  the 
  outer 
  

   reef 
  flat 
  about 
  4 
  miles 
  in 
  the 
  lagoon. 
  Similar 
  reef 
  flats 
  exist 
  

   in 
  Tahanea, 
  where 
  they 
  form 
  a 
  secondary 
  lagoon 
  with 
  2 
  to 
  

   3 
  fathoms 
  of 
  water, 
  extending 
  nearly 
  the 
  whole 
  length 
  of 
  the 
  

   western 
  face 
  of 
  the 
  atoll. 
  There 
  are 
  several 
  large 
  islands 
  on 
  

   this 
  flat 
  and 
  at 
  high 
  water 
  they 
  would 
  appear 
  as 
  the 
  islands 
  and 
  

   islets 
  of 
  Fakarava 
  do, 
  as 
  disconnected 
  and 
  planted 
  in 
  the 
  

   lagoon 
  itself. 
  A 
  secondary 
  lagoon 
  also 
  exists 
  in 
  Ravahere, 
  and 
  

   in 
  Anaa 
  ; 
  in 
  both 
  these 
  atolls 
  the 
  reef 
  flat 
  extends 
  across 
  one 
  

   extremity 
  of 
  the 
  lagoon 
  and 
  does 
  not 
  run 
  parallel 
  to 
  the 
  longer 
  

   shore-line 
  of 
  the 
  atoll. 
  

  

  The 
  lagoons 
  of 
  these 
  atolls 
  have 
  a 
  general 
  depth 
  of 
  13 
  to 
  20 
  

   fathoms. 
  In 
  some 
  cases 
  they 
  are 
  somewhat 
  deeper, 
  as 
  is 
  stated, 
  

   but 
  there 
  are 
  no 
  measurements, 
  the 
  greater 
  depths, 
  30 
  fathoms 
  

   or 
  more, 
  being 
  due 
  to 
  orogenic 
  conditions. 
  Some 
  of 
  the 
  atolls 
  

   are 
  quite 
  shallow, 
  as 
  at 
  Matahiva, 
  as 
  well 
  as 
  Pinaki, 
  where 
  the 
  

   lagoon 
  is 
  not 
  more 
  than 
  2 
  to 
  3 
  fathoms, 
  and 
  Takume, 
  where 
  it 
  

   is 
  from 
  5 
  to 
  6 
  fathoms 
  deep. 
  Some 
  of 
  the 
  smaller 
  islets 
  we 
  

   visited, 
  among 
  which 
  are 
  Tikei, 
  Aki-Aki, 
  and 
  Nukutavake, 
  

   have 
  no 
  lagoons. 
  The 
  former 
  has 
  a 
  small 
  shallow 
  sink 
  in 
  

   which 
  fresh 
  water 
  collects, 
  but 
  the 
  rim 
  is 
  only 
  very 
  slightly 
  

   higher 
  than 
  the 
  interior. 
  The 
  last 
  two 
  islets 
  are 
  apparently 
  

   depressed 
  in 
  the 
  center, 
  3 
  to 
  4 
  feet 
  below 
  the 
  outer 
  bank 
  of 
  

   sand 
  which 
  forms 
  the 
  rim 
  (about 
  10 
  to 
  12 
  feet 
  high) 
  of 
  the 
  

   basin 
  of 
  the 
  island. 
  I 
  was 
  at 
  first 
  inclined 
  to 
  look 
  upon 
  these 
  

   islands 
  as 
  examples 
  of 
  islands 
  which 
  had 
  been 
  cut 
  down 
  to 
  the 
  

   level 
  of 
  the 
  sea 
  and 
  subsequently 
  been 
  built 
  up 
  by 
  beach 
  rock 
  

   and 
  sand 
  in 
  the 
  manner 
  described 
  above. 
  The 
  existence 
  of 
  

   extensive 
  sand 
  dunes 
  on 
  two 
  sides 
  of 
  the 
  island 
  at 
  Pinaki, 
  and 
  

   of 
  a 
  large 
  dune 
  (estimated 
  to 
  be 
  35 
  feet 
  high) 
  on 
  the 
  south 
  

   shore 
  of 
  Nikutavake, 
  seems 
  to 
  indicate 
  the 
  possibility 
  of 
  there 
  

   having 
  been 
  a 
  shallow 
  lagoon 
  occupying 
  the 
  center 
  of 
  Aki-Aki 
  

   and 
  of 
  Nukutavake, 
  and 
  that 
  these 
  lagoons 
  were 
  gradually 
  

   filled 
  by 
  the 
  sand 
  dunes, 
  much 
  as 
  Pinaki 
  is 
  filling 
  now. 
  

  

  At 
  Pinaki 
  (Whitsunday 
  Island), 
  there 
  is 
  no 
  doubt 
  that 
  the 
  

   lagoon 
  is 
  rapidly 
  filling 
  from 
  the 
  sand 
  blown 
  in 
  by 
  the 
  dunes. 
  

   They 
  are 
  from 
  12 
  to 
  15 
  feet 
  high, 
  and 
  are 
  forcing 
  their 
  way 
  in 
  

  

  