﻿F. 
  A. 
  Perret 
  — 
  The 
  Ascent 
  of 
  Lava. 
  

  

  607 
  

  

  as 
  a 
  small, 
  compressed 
  plug. 
  Daly 
  has 
  pointed 
  out* 
  the 
  

   powerful 
  heating 
  effect 
  of 
  such 
  compression, 
  by 
  which 
  the 
  gas 
  

   acquires 
  a 
  true 
  fluxing 
  power, 
  melting 
  the 
  contact 
  walls. 
  The 
  

   fused 
  material 
  absorbs 
  gas, 
  adding 
  heat 
  of 
  solution 
  and 
  of 
  

   chemical 
  reaction. 
  The 
  gaseous 
  head 
  of 
  the 
  lava 
  column 
  thus 
  

   becomes 
  an 
  effective 
  means 
  of 
  progression, 
  capable 
  of 
  fluxing 
  

   its 
  way 
  through 
  the 
  hardest 
  strata. 
  Examples 
  of 
  this 
  action 
  

   on 
  a 
  small 
  scale 
  may 
  be 
  seen 
  in 
  the 
  many 
  little 
  pit-craters 
  at 
  

  

  Fig. 
  2. 
  

  

  Fig. 
  2. 
  Lava 
  column 
  with 
  expanding 
  gaseous 
  head, 
  eating 
  its 
  way 
  upward 
  

   through 
  incoherent 
  material. 
  

  

  Kilauea, 
  which 
  are 
  simple, 
  cylindrical 
  channels 
  rising 
  vertically 
  

   through 
  the 
  solid 
  lava 
  strata. 
  

  

  If, 
  on 
  the 
  other 
  hand, 
  the 
  ascent 
  of 
  lava 
  is 
  through 
  a 
  con- 
  

   glomerate 
  mass 
  of 
  more 
  or 
  less 
  incoherent 
  materials, 
  it 
  is 
  certain 
  

   that 
  the 
  gases 
  cannot 
  be 
  so 
  perfectly 
  retained 
  and 
  compressed 
  

   above 
  the 
  column 
  of 
  lava. 
  In 
  such 
  a 
  case 
  their 
  action 
  will 
  be 
  

   excavative, 
  disintegrative, 
  corrosive. 
  Channels 
  will 
  be 
  enlarged, 
  

   masses 
  dislodged 
  and 
  engulfed; 
  and 
  this 
  "stoping" 
  process 
  

   will 
  be 
  combined 
  with 
  the 
  peculiarly 
  destructive 
  effects 
  of 
  

   fumarolic 
  activity. 
  In 
  contradistinction 
  to 
  the 
  former 
  method 
  

   of 
  temperature 
  development, 
  this 
  is 
  here 
  maintained 
  by 
  the 
  

  

  * 
  Reginald 
  A. 
  Daly; 
  The 
  Nature 
  of 
  Volcanic 
  Action, 
  Proc. 
  Amer. 
  Acad. 
  

   Sci., 
  vol. 
  xlvii, 
  No. 
  3, 
  p. 
  93. 
  

  

  