﻿GEOLOGY 
  OF 
  MADAGASCAR. 
  329 
  

  

  resemblance 
  to 
  those 
  of 
  Archaean 
  regions 
  in 
  other 
  parts 
  of 
  the 
  

   world. 
  They 
  consist 
  of 
  enormous 
  bands 
  of 
  gneiss 
  (with 
  which 
  gra- 
  

   nite 
  is 
  frequently 
  associated), 
  accompanied 
  by 
  beds 
  of 
  magnetic 
  

   iron 
  ore, 
  haematite, 
  mica-schist, 
  clay-slate, 
  quartzite, 
  crystalline 
  

   limestone, 
  serpentine, 
  hornblende-rock, 
  graphite, 
  &c. 
  Indeed, 
  

   throughout 
  this 
  extensive 
  region 
  all 
  the 
  rocks 
  appear 
  to 
  belong 
  

   to 
  the 
  crystalline 
  series 
  ; 
  they 
  are, 
  moreover, 
  so 
  far 
  as 
  is 
  known, 
  

   unfossiliferous, 
  though 
  what 
  may 
  await 
  future 
  discovery 
  it 
  is 
  

   impossible 
  to 
  say. 
  In 
  the 
  present 
  state 
  of 
  our 
  knowledge, 
  therefore, 
  

   of 
  the 
  geology 
  of 
  the 
  eastern 
  half 
  of 
  Madagascar, 
  we 
  can 
  only 
  say 
  

   with 
  certainty 
  that 
  the 
  rocks 
  of 
  this 
  region 
  belong 
  to 
  the 
  crystalline 
  

   series, 
  and 
  that, 
  judging 
  from 
  their 
  close 
  resemblance, 
  in 
  character 
  

   and 
  mode 
  of 
  occurrence, 
  to 
  the 
  Archaean 
  rocks 
  of 
  North 
  America, 
  

   Scandinavia, 
  and 
  the 
  Scottish 
  Highlands, 
  they 
  will 
  probably 
  here- 
  

   after 
  prove 
  to 
  be 
  Archaean. 
  But 
  with 
  these 
  there 
  may 
  not 
  unlikely 
  

   be 
  found 
  highly 
  metamorphosed 
  Cambrian 
  and 
  Silurian 
  strata. 
  

  

  That 
  this 
  part 
  of 
  the 
  island 
  has 
  been 
  above 
  the 
  sea 
  for 
  an 
  immense 
  

   period 
  is 
  shown 
  by 
  the 
  fact 
  of 
  its 
  rooks 
  having 
  supplied 
  the 
  material 
  

   which 
  formed 
  the 
  extensive 
  Jurassic, 
  Cretaceous, 
  and 
  Eocene 
  beds 
  

   to 
  the 
  west, 
  which 
  lie 
  on 
  them 
  unconformably, 
  as 
  also 
  by 
  the 
  exten- 
  

   sive 
  denudation 
  they 
  have 
  undergone. 
  It 
  may 
  therefore 
  confidently 
  

   be 
  said 
  that 
  the 
  eastern 
  half 
  of 
  the 
  island 
  has 
  been 
  dry 
  land 
  at 
  least 
  

   since 
  early 
  Mesozoic 
  times. 
  The 
  forces 
  which 
  have 
  elevated 
  the 
  

   island 
  have 
  probably 
  been 
  chiefly 
  concentrated 
  on 
  the 
  eastern 
  side. 
  

   This 
  is 
  shown 
  by 
  that 
  side 
  being 
  much 
  steeper 
  than 
  the 
  western, 
  

   and 
  by 
  the 
  fact 
  that 
  the 
  dominant 
  dip 
  of 
  the 
  rocks 
  is 
  towards 
  the 
  

   west. 
  Further 
  investigation 
  will 
  almost 
  certainly 
  reveal 
  the 
  exist- 
  

   ence 
  of 
  numerous 
  faults 
  running 
  in 
  a 
  direction 
  parallel 
  with 
  the 
  

   east 
  coast 
  of 
  the 
  island. 
  One 
  of 
  these 
  faults 
  not 
  improbably 
  exists 
  

   at 
  the 
  western 
  edge 
  of 
  the 
  great 
  Ankay 
  and 
  Antsihanaka 
  plains, 
  

   another 
  immediately 
  to 
  the 
  west 
  of 
  the 
  capital, 
  and 
  another 
  about 
  

   long. 
  47°. 
  If 
  we 
  may 
  take 
  the 
  fringing 
  coral-reefs 
  *, 
  which 
  

   surround 
  the 
  island 
  for 
  the 
  most 
  part, 
  as 
  implying 
  non-subsidence, 
  

   and 
  the 
  absence 
  of 
  ancient 
  sea-beaches 
  or 
  recent 
  marine 
  deposits 
  

  

  * 
  Mr. 
  Wallace, 
  in 
  his 
  ' 
  Island 
  Life,' 
  p. 
  386, 
  says: 
  — 
  "We 
  have 
  also 
  evidence 
  

   that 
  it 
  [Madagascar] 
  has 
  recently 
  been 
  considerably 
  larger 
  ; 
  for 
  along 
  the 
  east 
  

   coast 
  there 
  is 
  an 
  extensive 
  barrier 
  coral-reef 
  about 
  350 
  miles 
  in 
  length, 
  and 
  

   varying 
  in 
  distance 
  from 
  the 
  land 
  from 
  a 
  quarter 
  of 
  a 
  mile 
  to 
  three 
  or 
  four 
  

   miles. 
  This 
  is 
  good 
  proof 
  of 
  recent 
  subsidence 
  ; 
  while 
  we 
  have 
  no 
  record 
  of 
  

   raised 
  coral 
  rocks 
  inland 
  which 
  would 
  certainly 
  mark 
  any 
  recent 
  elevation, 
  

   because 
  fringing 
  coral-reefs 
  surround 
  a 
  considerable 
  portion 
  of 
  the 
  northern, 
  

   eastern, 
  and 
  south-western 
  coast." 
  From 
  this 
  it 
  would 
  seem 
  that 
  both 
  barrier 
  

   and 
  /ringing-reefs 
  are 
  found 
  on 
  the 
  east 
  coast. 
  But, 
  if 
  I 
  am 
  not 
  greatly 
  mis- 
  

   taken, 
  these 
  reefs 
  are, 
  at 
  any 
  rate 
  for 
  the 
  most 
  part, 
  f 
  ringing-reefs. 
  As 
  for 
  the 
  

   raised 
  coral 
  rocks, 
  there 
  are 
  such 
  in 
  the 
  south-west 
  of 
  the 
  island 
  to 
  the 
  north 
  of 
  

   the 
  river 
  Onilahy, 
  about 
  twenty 
  miles 
  inland 
  on 
  the 
  road 
  to 
  Manja 
  ; 
  in 
  fact 
  they 
  

   exist, 
  it 
  seems, 
  throughout 
  the 
  southern 
  part 
  of 
  the 
  island. 
  On 
  some 
  parts 
  of 
  

   the 
  east 
  coast 
  the 
  sea 
  has 
  recently 
  but 
  gradually 
  receded 
  several 
  miles, 
  but 
  this 
  

   seems 
  to 
  be 
  owing 
  to 
  the 
  heaping 
  up 
  of 
  sand 
  by 
  the 
  sea, 
  aided 
  by 
  the 
  wind, 
  rather 
  

   than 
  to 
  elevation 
  of 
  the 
  land. 
  Sand 
  and 
  pebbles 
  thus 
  left 
  by 
  the 
  sea 
  may 
  be 
  

   seen 
  as 
  far 
  inland 
  as 
  the 
  foot 
  of 
  Manjakandritinombana, 
  some 
  four 
  or 
  five 
  miles 
  

   west 
  of 
  Tamatave. 
  

  

  