﻿112 
  Agassis 
  — 
  Explorations 
  of 
  the 
  "Albatross." 
  

  

  with 
  scattered 
  islets 
  and 
  atolls 
  extending 
  from 
  Mangareva 
  to 
  

   Pinaki, 
  and 
  northward 
  to 
  Serle 
  Island 
  and 
  beyond, 
  islands 
  

   which 
  are 
  not 
  connected 
  with 
  the 
  extensive 
  plateau 
  upon 
  

   which 
  the 
  greater 
  number 
  of 
  the 
  Paumotu 
  Islands 
  to 
  the 
  west- 
  

   ward 
  of 
  Hao 
  rise. 
  

  

  All 
  the 
  islands 
  we 
  have 
  examined 
  are, 
  without 
  exception,, 
  

   formed 
  of 
  Tertiary 
  coralliferous 
  limestone 
  which 
  has 
  been 
  

   elevated 
  to 
  a 
  greater 
  or 
  less 
  extent 
  above 
  the 
  level 
  of 
  the 
  sea, 
  

   and 
  then 
  planed 
  down 
  by 
  atmospheric 
  agencies 
  and 
  submarine 
  

   erosion, 
  the 
  greatest 
  elevation 
  being 
  at 
  Makatea 
  (about 
  230 
  

   feet), 
  and 
  at 
  Niau, 
  where 
  the 
  Tertiary 
  coralliferous 
  limestone 
  

   does 
  not 
  rise 
  to 
  a 
  greater 
  height 
  than 
  20 
  feet. 
  At 
  Rairoa 
  it 
  

   was 
  15 
  to 
  16 
  feet 
  high. 
  At 
  other 
  islands 
  it 
  could 
  be 
  traced 
  

   only 
  as 
  forming 
  the 
  shore 
  platform, 
  from 
  50 
  to 
  150 
  feet 
  wide, 
  

   which 
  forms 
  the 
  outer 
  face 
  of 
  the 
  Panmotus 
  and 
  is 
  so 
  charac- 
  

   teristic 
  a 
  feature 
  of 
  the 
  atolls 
  of 
  the 
  group. 
  In 
  other 
  parts 
  

   the 
  old 
  ledge 
  could 
  be 
  traced 
  cropping 
  up 
  in 
  the 
  interior 
  of 
  the 
  

   outer 
  rim, 
  or 
  in 
  the 
  open 
  cuts 
  connecting 
  the 
  lagoon 
  with 
  the 
  

   outer 
  sea 
  face 
  of 
  the 
  atolls. 
  Everywhere 
  the 
  space 
  between 
  

   the 
  outcropping 
  of 
  the 
  old 
  ledge, 
  as 
  I 
  will 
  call 
  the 
  Tertiary 
  

   coralliferous 
  limestone, 
  was 
  filled 
  with 
  beach 
  rock, 
  or 
  a 
  pud- 
  

   ding-stone, 
  or 
  with 
  a 
  breccia 
  or 
  conglomerate 
  of 
  coralliferous 
  

   material 
  consisting 
  in 
  part 
  of 
  fragments 
  of 
  the 
  old 
  ledge, 
  and 
  

   of 
  fragments 
  of 
  recent 
  corals 
  and 
  shells 
  cemented 
  together. 
  

  

  The 
  appearance 
  of 
  the 
  old 
  ledge 
  and 
  of 
  the 
  modern 
  reef 
  

   rock 
  is 
  so 
  strikingly 
  different 
  that 
  it 
  is 
  very 
  simple 
  to 
  distinguish 
  

   the 
  two, 
  even 
  where 
  only 
  comparatively 
  small 
  fragments 
  are 
  

   found. 
  

  

  We 
  did 
  not 
  find 
  in 
  the 
  Paumotus, 
  as 
  in 
  Fiji, 
  all 
  possible 
  

   stages 
  of 
  denudation 
  and 
  of 
  submarine 
  erosion 
  between 
  islands 
  

   like 
  Vatu 
  Yara, 
  Niau, 
  Kambara, 
  Fulanga, 
  Ongea, 
  Oneata, 
  

   Ngele 
  Levu, 
  and 
  Weilangilala, 
  and 
  atolls 
  with 
  a 
  mere 
  ring 
  of 
  

   surf 
  to 
  indicate 
  their 
  existence. 
  

  

  In 
  the 
  Paumotus 
  the 
  islands 
  have 
  been 
  elevated 
  to 
  a 
  very 
  

   moderate 
  height 
  and 
  probably 
  to 
  nearly 
  the 
  same 
  height, 
  for 
  

   the 
  old 
  ledge 
  forming 
  the 
  base 
  of 
  the 
  modern 
  structure 
  is 
  found 
  

   exposed 
  nearly 
  everywhere 
  at 
  about 
  low-water 
  when 
  it 
  cannot 
  

   be 
  traced 
  at 
  a 
  slightly 
  greater 
  elevation. 
  This 
  would 
  readily 
  

   account 
  for 
  the 
  nearly 
  uniform 
  height 
  of 
  the 
  islands 
  through- 
  

   out 
  the 
  group. 
  

  

  But 
  there 
  is 
  another 
  element 
  which 
  comes 
  into 
  play 
  in 
  this 
  

   group, 
  and 
  has 
  an 
  important 
  part 
  in 
  shaping 
  the 
  ultimate 
  con- 
  

   dition 
  of 
  these 
  atolls. 
  At 
  the 
  Fijis 
  we 
  have 
  seen 
  the 
  subma- 
  

   rine 
  erosion 
  continue 
  until 
  there 
  is 
  little 
  left 
  of 
  many 
  of 
  the 
  

   atolls 
  beyond 
  the 
  merest 
  small 
  islet 
  or 
  rock 
  to 
  indicate 
  its 
  struc- 
  

   ture. 
  In 
  the 
  Paumotus, 
  in 
  the 
  great 
  atolls 
  which 
  are 
  evidently 
  

   only 
  the 
  exposed 
  summits 
  of 
  parts 
  of 
  ridges 
  or 
  spurs 
  of 
  an 
  

  

  