﻿346 
  W. 
  G. 
  Foye 
  — 
  Geology 
  of 
  the 
  Lau 
  Islands. 
  

  

  of 
  the 
  upper 
  curve. 
  Here, 
  near 
  the 
  center 
  of 
  the 
  island, 
  is 
  

   situated 
  its 
  highest 
  peak, 
  Koro 
  Mbasanga, 
  which 
  rises 
  930 
  feet. 
  

   North 
  of 
  this 
  peak 
  the 
  country 
  slopes 
  down 
  in 
  wide, 
  spoon- 
  

   shaped 
  valleys 
  to 
  a 
  limestone 
  platform, 
  having 
  a 
  broken 
  surface 
  

   which 
  forms 
  the 
  northern 
  end 
  of 
  the 
  island. 
  The 
  average 
  

   elevation 
  of 
  the 
  platform 
  is 
  350 
  feet. 
  It 
  swings 
  southward 
  on 
  

   the 
  western 
  side 
  of 
  Koro 
  Mbasanga 
  and 
  terminates 
  just 
  west 
  

   of 
  the 
  peak, 
  wedging 
  out 
  along 
  the 
  shore. 
  

  

  Southward 
  from 
  this 
  peak 
  a 
  broken 
  ridge 
  forms 
  a 
  serrate 
  

   backbone 
  to 
  the 
  island. 
  The 
  map 
  shows 
  hills 
  500 
  and 
  700 
  feet 
  

   high 
  along 
  this 
  ridge, 
  but 
  the 
  usual 
  altitude 
  is 
  but 
  300 
  or 
  400 
  

   feet. 
  The 
  hills 
  are 
  low 
  and 
  rounded. 
  

  

  At 
  the 
  southern 
  end 
  of 
  the 
  island 
  the 
  low 
  ridge 
  dips 
  south- 
  

   ward 
  beneath 
  a 
  small 
  area 
  of 
  limestone 
  standing 
  at 
  an 
  elevation 
  

   of 
  about 
  300 
  feet. 
  The 
  peak, 
  Koro 
  Mbasanga, 
  has 
  an 
  amphi- 
  

   theater-like 
  depression 
  on 
  its 
  eastern 
  side. 
  The 
  southern 
  limb 
  

   of 
  the 
  ridge 
  inclosing 
  the 
  amphitheater 
  was 
  followed 
  south- 
  

   ward 
  and 
  it 
  was 
  found 
  that 
  lavas 
  from 
  this 
  peak 
  had 
  over- 
  

   flowed 
  an 
  area 
  of 
  limestone 
  and 
  baked 
  it 
  red. 
  The 
  limestone 
  

   was 
  a 
  foraminiferal 
  variety 
  containing 
  little 
  or 
  no 
  coral. 
  Just 
  

   north 
  of 
  Koro 
  Mbasanga 
  a 
  similar 
  limestone, 
  but 
  silver-grey 
  in 
  

   color, 
  was 
  found 
  in 
  patches 
  overlying 
  an 
  eroded 
  volcanic 
  sur- 
  

   face. 
  Here 
  it 
  included 
  bits 
  of 
  the 
  underlying 
  rock 
  and 
  formed 
  

   an 
  undoubted 
  basal 
  layer. 
  

  

  From 
  the 
  facts 
  just 
  recorded 
  it 
  was 
  inferred 
  that 
  an 
  eroded 
  

   surface 
  of 
  volcanic 
  rocks 
  had 
  been 
  submerged 
  and 
  overlain 
  

   unconformably 
  by 
  limestone. 
  The 
  evidence 
  was 
  inconclusive, 
  

   however, 
  as 
  to 
  whether 
  the 
  limestone 
  had 
  been 
  elevated 
  and 
  

   eroded 
  before 
  the 
  extrusion 
  of 
  the 
  volcanic 
  rocks 
  of 
  the 
  second 
  

   period. 
  This 
  question 
  was 
  answered 
  by 
  exposures 
  in 
  the 
  small 
  

   island 
  of 
  Andivathi, 
  lying 
  off 
  the 
  northwestern 
  coast 
  of 
  Vanua 
  

   Mbalavu 
  within 
  the 
  upper 
  curve 
  of 
  the 
  question 
  mark. 
  

  

  The 
  larger 
  part 
  of 
  Andivathi 
  is 
  composed 
  of 
  andesite 
  agglom- 
  

   erate 
  and 
  ash 
  dipping 
  30° 
  E. 
  The 
  western 
  beds, 
  representing 
  

   the 
  lower 
  members 
  of 
  the 
  series, 
  are 
  of 
  coarse 
  agglomerate 
  

   with 
  vesicular 
  blocks 
  of 
  lava 
  a 
  foot 
  or 
  more 
  in 
  diameter. 
  The 
  

   upper 
  beds 
  become 
  increasingly 
  finer 
  and 
  show 
  many 
  small 
  

   fragments 
  of 
  pumice. 
  The 
  total 
  thickness 
  of 
  these 
  beds 
  is 
  

   about 
  200 
  feet. 
  The 
  eastern 
  side 
  of 
  Andivathi 
  is 
  composed 
  of 
  

   elevated 
  coraliferous 
  limestone. 
  Both 
  ash 
  and 
  limestone 
  are 
  

   cut 
  by 
  a 
  network 
  of 
  basic 
  dikes, 
  the 
  largest 
  observed 
  being 
  20 
  

   feet 
  in 
  width. 
  It 
  is 
  deeply 
  lateritized 
  and 
  outcrops 
  as 
  a 
  long, 
  

   well-denned 
  depression 
  in 
  the 
  limestone 
  into 
  which 
  it 
  was 
  in- 
  

   truded. 
  The 
  limestone 
  stands 
  up 
  in 
  nearly 
  perpendicular 
  walls 
  

   on 
  either 
  side 
  of 
  the 
  depression 
  which 
  was 
  once 
  filled 
  with 
  the 
  

   dike, 
  indicating 
  that 
  in 
  this 
  climate 
  the 
  igneous 
  rock 
  weathers 
  

   more 
  rapidly 
  than 
  the 
  sedimentary. 
  On 
  the 
  N.E. 
  side 
  of 
  

  

  