﻿F. 
  A. 
  Pervet—The 
  Ascent 
  of 
  Lava. 
  605 
  

  

  Art. 
  LIII. 
  — 
  The 
  Ascent 
  of 
  Lava 
  / 
  by 
  Frank 
  A. 
  Perret. 
  

  

  Why 
  does 
  the 
  lava 
  rise 
  from 
  below 
  toward 
  the 
  earth's 
  

   surface 
  ? 
  

  

  This 
  fundamental 
  question 
  resolves 
  itself, 
  upon 
  examina- 
  

   tion, 
  into 
  several 
  parts. 
  We 
  may 
  ask, 
  for 
  instance, 
  why 
  the 
  

   lava 
  should 
  move 
  in 
  any 
  direction, 
  — 
  why, 
  that 
  is 
  to 
  say, 
  there 
  

   should 
  be 
  motion 
  of 
  translation 
  in 
  this 
  material, 
  — 
  why 
  it 
  should 
  

   seek 
  to 
  extend 
  itself 
  from 
  the 
  position 
  it 
  occupies? 
  But, 
  — 
  

   whether 
  by 
  reason 
  of 
  the 
  pressure 
  to 
  which 
  it 
  may 
  be 
  sub- 
  

   jected, 
  or 
  through 
  actual 
  augmentation 
  of 
  its 
  substance, 
  or 
  

   by 
  the 
  absorption 
  of 
  infiltrating 
  materials, 
  or 
  even 
  through 
  

   greater 
  fluidity 
  resulting 
  from 
  some 
  lessening 
  of 
  pressures, 
  — 
  

   we 
  know 
  the 
  magma 
  to 
  be 
  endowed 
  with 
  the 
  property 
  and 
  

   power 
  of 
  expansivity, 
  in 
  consequence 
  of 
  which 
  it 
  must, 
  if 
  pos- 
  

   sible, 
  find 
  or 
  form 
  for 
  itself 
  an 
  outlet 
  through 
  its 
  too 
  restrict- 
  

   ing 
  boundaries. 
  

  

  Nor, 
  in 
  view 
  of 
  this 
  quality 
  of 
  expansiveness, 
  shall 
  we 
  mar- 
  

   vel 
  that 
  the 
  magma 
  should 
  rise 
  into 
  a 
  fissure 
  which 
  may 
  open 
  

   above 
  the 
  stratum 
  or 
  pocket 
  which 
  constitutes 
  the 
  reservoir. 
  

   Assuming 
  such 
  injections 
  to 
  be 
  abyssal, 
  they 
  will 
  not, 
  in 
  gen- 
  

   eral, 
  perforate 
  the 
  outermost 
  shells 
  but, 
  whether 
  remaining 
  as 
  

   simple, 
  lava-filled 
  rifts 
  or 
  developing 
  the 
  expanded, 
  top-like 
  

   sections 
  imagined 
  by 
  Johnston-Lavis* 
  and 
  Daly,t 
  they 
  will 
  

   constitute 
  secondary 
  reservoirs 
  nearer 
  to, 
  but 
  not 
  yet 
  in 
  com- 
  

   munication 
  with, 
  the 
  surface. 
  It 
  is 
  from 
  this 
  point 
  that 
  the 
  

   further 
  progress 
  of 
  the 
  lava 
  forms 
  the 
  subject 
  of 
  our 
  inquiry, 
  — 
  

   why, 
  of 
  all 
  possible 
  directions, 
  this 
  should 
  still 
  be 
  upward 
  or, 
  

   more 
  precisely, 
  outward 
  from 
  the 
  direction 
  of 
  the 
  earth's 
  center 
  

   toward 
  its 
  periphery 
  ? 
  

  

  Such 
  further 
  progress 
  is 
  effected, 
  in 
  general, 
  by 
  a 
  progress 
  

   of 
  trepanning^ 
  so 
  to 
  speak, 
  which 
  results 
  in 
  the 
  formation 
  of 
  a 
  

   vertical 
  tunnel, 
  often 
  of 
  exceedingly 
  small 
  diameter 
  in 
  propor- 
  

   tion 
  to 
  its 
  length. 
  

  

  But, 
  if 
  we 
  remember 
  that 
  the 
  rising 
  of 
  the 
  lava 
  represents 
  

   work 
  against 
  gravity 
  and 
  necessitates 
  the 
  perforation 
  of 
  succes- 
  

   sive 
  strata, 
  and 
  that, 
  furthermore, 
  the 
  progression 
  takes 
  place 
  

   at 
  the 
  point 
  farthest 
  from 
  the 
  heat 
  reservoir 
  and 
  where 
  the 
  

   actual 
  contact 
  pressure 
  is 
  least, 
  it 
  would 
  almost 
  appear, 
  at 
  first 
  

   sight, 
  that, 
  in 
  ascending 
  as 
  it 
  does, 
  the 
  lava 
  follows 
  the 
  path 
  of 
  

   greatest 
  resistance 
  and 
  advances 
  where 
  its 
  power 
  to 
  do 
  so 
  is 
  

   most 
  limited. 
  

  

  * 
  H. 
  J. 
  Johnston-Lavis 
  : 
  The 
  Mechanism 
  of 
  Volcanic 
  Action, 
  Geological 
  

   Magazine, 
  London, 
  October, 
  1909. 
  

  

  fEeginald 
  A. 
  Daly: 
  Abyssal 
  Injection 
  as 
  a 
  Causal 
  Condition 
  and 
  as 
  an 
  

   Effect 
  of 
  Mountain-Bnilding, 
  this 
  Journal, 
  Sept., 
  1906. 
  

  

  