﻿228 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OP 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  9 
  

  

  ejecta, 
  highly 
  vesiculated, 
  containing 
  large 
  amounts 
  of 
  glassy 
  material, 
  

   ejected 
  by 
  violent 
  explosions 
  following 
  long 
  periods 
  of 
  quiescence. 
  

   The 
  well-known 
  cases 
  of 
  Bandai-San, 
  Krakatoa, 
  and 
  Martinique 
  may 
  

   be 
  cited 
  as 
  illustrations. 
  Material 
  ejected 
  from 
  Krakatoa 
  "was 
  

   so 
  vesicular 
  that 
  it 
  floated 
  in 
  the 
  water, 
  accumulating 
  here 
  and 
  there 
  

   in 
  great 
  banks 
  which 
  covered 
  the 
  sea 
  for 
  miles, 
  rising 
  sometimes 
  to 
  a 
  

   height 
  of 
  four 
  or 
  five 
  feet 
  above 
  it,"^ 
  and 
  the 
  ejecta 
  still 
  contained 
  

   considerable 
  water, 
  as 
  well 
  as 
  much 
  glassy 
  material. 
  

  

  In 
  the 
  above 
  discussion 
  the 
  question 
  of 
  the 
  source 
  of 
  the 
  water 
  has 
  

   not 
  been 
  considered. 
  Doubtless 
  the 
  original 
  magmas 
  contain 
  water, 
  

   but 
  whether 
  or 
  not 
  this 
  is 
  augmented 
  by 
  accession 
  of 
  meteoric 
  water 
  

   is 
  an 
  open 
  question. 
  The 
  often 
  cited 
  proximity 
  of 
  active 
  vol- 
  

   canoes 
  to 
  large 
  bodies 
  of 
  water 
  may 
  be 
  regarded 
  as 
  evidence 
  of 
  

   the 
  probability 
  of 
  such 
  accession, 
  and 
  in 
  some 
  instances 
  the 
  case 
  for 
  

   the 
  absorption 
  of 
  meteoric 
  water 
  is 
  strong, 
  but 
  it 
  may 
  not 
  be 
  true 
  in 
  

   the 
  majority 
  of 
  cases. 
  It 
  has 
  been 
  demonstrated 
  by 
  Johnston 
  and 
  

   Adams^ 
  that 
  the 
  phenomenon 
  of 
  capillarity 
  does 
  not 
  furnish 
  a 
  mechan- 
  

   ism 
  for 
  the 
  introduction 
  of 
  water 
  into 
  magmas, 
  and 
  they 
  have 
  shown 
  

   that 
  the 
  often 
  cited 
  Daubree 
  experiment 
  has 
  no 
  bearing 
  on 
  the 
  ques- 
  

   tion 
  at 
  issue. 
  As 
  previously 
  stated, 
  crystallization 
  and 
  differentia- 
  

   tion 
  will 
  result 
  in 
  the 
  accumulation 
  of 
  water 
  in 
  the 
  residual 
  magma, 
  

   and 
  such 
  accumulation 
  probably 
  is 
  competent 
  to 
  explain 
  the 
  produc- 
  

   tion 
  of 
  those 
  pitchstones 
  which 
  contain 
  water 
  sometimes 
  up 
  to 
  10 
  

   per 
  cent. 
  Irrespective 
  of 
  the 
  relative 
  importance 
  of 
  original 
  and 
  me- 
  

   teoric 
  water, 
  it 
  is 
  believed 
  that 
  the 
  relations 
  which 
  have 
  been 
  outlined 
  

   furnish 
  a 
  mechanism 
  by 
  which 
  water 
  can 
  enter 
  a 
  magma. 
  Not 
  only 
  

   is 
  it 
  possible 
  for 
  a 
  magma 
  to 
  take 
  up 
  water, 
  but 
  the 
  water 
  ma}' 
  be 
  taken 
  

   up 
  by 
  the 
  magma 
  under 
  a 
  small 
  pressure 
  head 
  and 
  later 
  liberated 
  with 
  

   the 
  development 
  of 
  high 
  pressure. 
  

  

  It 
  has 
  already 
  been 
  shown 
  that 
  in 
  a 
  crystallizing 
  magma 
  the 
  water 
  

   accumulates 
  in 
  the 
  liquid 
  phase. 
  If 
  a 
  magma, 
  either 
  deficient 
  in 
  water 
  

   or 
  containing 
  but 
  a 
  small 
  amount 
  of 
  water, 
  and 
  above 
  its 
  crystallizing 
  

   temperature, 
  be 
  in 
  contact 
  with 
  porous 
  water-containing 
  strata, 
  it 
  will 
  

   absorb 
  water 
  vapor 
  until 
  its 
  water 
  content 
  corresponds 
  to 
  the 
  pre- 
  

   vailing 
  temperature 
  of 
  the 
  magma 
  and 
  to 
  the 
  pressure 
  of 
  water 
  vapor. 
  

   The 
  portion 
  of 
  such 
  a 
  stratum 
  near 
  the 
  volcanic 
  neck 
  will 
  be 
  at 
  a 
  high 
  

   temperature, 
  and 
  the 
  water 
  in 
  this 
  portion 
  will 
  be 
  in 
  the 
  form 
  of 
  steam; 
  

   the 
  cooler 
  portions 
  farther 
  removed 
  will 
  contain 
  liquid 
  water, 
  and 
  be- 
  

  

  ^ 
  T. 
  G. 
  BONNEY, 
  Volcanoes, 
  p. 
  24. 
  The 
  Science 
  Series. 
  G. 
  P. 
  Putnam's 
  Sons, 
  1899. 
  

   * 
  J. 
  Johnston 
  and 
  L. 
  H. 
  Adams. 
  Journ. 
  Geol. 
  22: 
  1-15. 
  1914. 
  

  

  