﻿216 
  PEOF. 
  J. 
  W. 
  JUDD 
  OX 
  THE 
  TEE1IAET 
  VOLCANOES 
  

  

  the 
  sea 
  " 
  [that 
  is 
  distances 
  of 
  from 
  30 
  to 
  40 
  miles 
  !], 
  " 
  spreading 
  out 
  

   from 
  a 
  quarter 
  of 
  a 
  mile 
  to 
  two 
  or 
  three 
  miles 
  in 
  width. 
  Upon 
  

   such 
  a 
  broad 
  surface 
  as 
  that 
  of 
  Manua 
  Loa 
  it 
  must 
  necessarily 
  

   happen 
  that 
  some 
  portions 
  may 
  lie 
  for 
  centuries 
  unscathed 
  by 
  lire, 
  

   and 
  during 
  this 
  period 
  of 
  immunity 
  the 
  lavas 
  decay, 
  soil 
  is 
  formed 
  

   upon 
  them 
  and 
  accumulates 
  to 
  the 
  depth 
  of 
  many 
  feet 
  "*. 
  

  

  The 
  facts 
  which 
  I 
  observed 
  in 
  the 
  Western 
  Isles 
  of 
  Scotland 
  led 
  

   me, 
  in 
  1874, 
  to 
  state 
  in 
  very 
  similar 
  terms 
  the 
  real 
  nature 
  of 
  the 
  

   basaltic 
  plateaux 
  of 
  that 
  district. 
  I 
  wrote 
  as 
  follows 
  : 
  — 
  

  

  " 
  The 
  whole 
  of 
  these 
  facts 
  point 
  to 
  the 
  conclusion 
  that, 
  during 
  

   the 
  period 
  of 
  the 
  emission 
  of 
  the 
  great 
  lava-floods 
  which 
  form 
  the 
  

   enormous 
  plateaux 
  of 
  the 
  Hebrides 
  and 
  Antrim, 
  the 
  surfaces 
  over 
  

   which 
  they 
  flowed 
  were 
  above 
  the 
  sea-level, 
  and, 
  further, 
  that 
  

   intervals 
  of 
  sufficient 
  duration 
  occurred 
  between 
  the 
  outpourings 
  

   of 
  the 
  lava-streams 
  to 
  admit 
  of 
  the 
  formation 
  of 
  those 
  very 
  

   interesting 
  intercalated 
  deposits, 
  which 
  are 
  in 
  every 
  case 
  of 
  a 
  

   terrestrial, 
  fluviatile, 
  or 
  lacustrine 
  origin 
  "t. 
  

  

  The 
  study 
  of 
  the 
  Hawaian 
  volcanoes 
  by 
  Captain 
  Dutton, 
  and 
  

   especially 
  by 
  Professor 
  Dana, 
  has 
  thrown 
  much 
  new 
  light 
  upon 
  

   certain 
  phases 
  of 
  volcanic 
  activity 
  ; 
  but 
  the 
  formation 
  of 
  great 
  

   plateaux 
  built 
  up 
  by 
  successive 
  outpourings 
  of 
  lava 
  of 
  basaltic 
  com- 
  

   position 
  and 
  of 
  great 
  liquidity 
  had 
  been 
  long 
  before 
  fully 
  recog- 
  

   nized 
  by 
  Air. 
  Scrope 
  and 
  other 
  vulcanologi?ts. 
  

  

  I 
  have 
  no 
  wish 
  to 
  suggest 
  that 
  the 
  great 
  volcanoes 
  of 
  the 
  Western 
  

   Isles 
  of 
  Scotland 
  were 
  of 
  the 
  same 
  type 
  as 
  those 
  of 
  the 
  Sandwich 
  

   Islands. 
  On 
  the 
  contrary, 
  I 
  believe 
  that 
  there 
  is 
  ample 
  evidence 
  

   to 
  show 
  that, 
  while 
  the 
  great 
  basaltic 
  plateaux 
  which 
  surround 
  those 
  

   volcanoes 
  were 
  built 
  up 
  by 
  successive 
  outflows 
  of 
  very 
  liquid 
  lava 
  

   from 
  their 
  summits 
  and 
  flanks, 
  yet 
  a 
  considerable 
  amount 
  of 
  explosive 
  

   action, 
  indicated 
  by 
  many 
  relics 
  of 
  great 
  masses 
  of 
  tuffs, 
  took 
  place 
  

   both 
  at 
  the 
  central 
  craters 
  and 
  from 
  the 
  parasitical 
  vents. 
  

  

  The 
  eruption 
  of 
  the 
  basaltic 
  lavas 
  was 
  preceded, 
  and 
  to 
  some 
  

   extent 
  accompanied 
  by 
  the 
  extrusion 
  of 
  lavas 
  of 
  more 
  acid 
  composi- 
  

   tion 
  — 
  audesites, 
  dacites, 
  and 
  rhyolites 
  ; 
  but 
  these 
  lavas, 
  as 
  I 
  showed, 
  

   were 
  generally 
  wanting 
  in 
  the 
  great 
  liquidity 
  which 
  characterized 
  

   the 
  basaltic 
  extrusions, 
  and 
  so 
  are, 
  for 
  the 
  most 
  part, 
  found 
  confined 
  

   to 
  the 
  immediate 
  vicinity 
  of 
  the 
  great 
  eruptive 
  centres. 
  

  

  During 
  fifteen 
  years 
  I 
  have 
  devoted 
  my 
  attention 
  to 
  the 
  study 
  

   of 
  the 
  varied 
  products 
  of 
  these 
  great 
  volcanoes 
  of 
  the 
  Western 
  Isles 
  

   of 
  Scotland, 
  and 
  I 
  have 
  again 
  and 
  again 
  revisited 
  them 
  to 
  clear 
  up 
  

   difficulties 
  as 
  they 
  arose 
  in 
  the 
  course 
  of 
  those 
  studies. 
  Many 
  errors 
  

   in 
  points 
  of 
  detail 
  I 
  am 
  prepared 
  to 
  admit, 
  but 
  of 
  the 
  truth 
  of 
  the 
  

   main 
  propositions 
  enunciated 
  in 
  my 
  memoir 
  I 
  have 
  become 
  more 
  

   and 
  more 
  convinced, 
  the 
  longer 
  I 
  have 
  studied 
  the 
  subject. 
  

  

  If 
  such 
  large 
  quantities 
  of 
  volcanic 
  material, 
  both 
  of 
  acid 
  and 
  basic 
  

   composition, 
  were 
  transferred 
  from 
  the 
  interior 
  of 
  the 
  earth's 
  crust 
  

   to 
  the 
  surface, 
  then 
  surely 
  we 
  ought 
  to 
  find, 
  in 
  a 
  greatly 
  denuded 
  

   area, 
  the 
  traces 
  of 
  those 
  conduits 
  and 
  channels 
  by 
  which 
  the 
  igneous 
  

  

  * 
  Fourth 
  Report 
  U. 
  S. 
  Geol. 
  Survey, 
  p. 
  93. 
  

  

  f 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxx. 
  (1S74), 
  p. 
  230. 
  

  

  