﻿VALLEY 
  OF 
  THE 
  ALIGNON 
  — 
  JAUJAC. 
  11 
  

  

  and 
  will 
  shoot 
  outwards, 
  so 
  as 
  to 
  form 
  simultaneously 
  at 
  points 
  equidistant 
  from 
  

   that 
  surface. 
  The 
  accuracy 
  of 
  the 
  empirical 
  law 
  is 
  greater 
  than 
  any 
  theoretical 
  

   view 
  could 
  possibly 
  lead 
  us 
  to 
  expect. 
  Varied 
  examples 
  will 
  be 
  quoted 
  in 
  the 
  

   following 
  pages. 
  

  

  A 
  little 
  way 
  above 
  La 
  Beaume, 
  near 
  the 
  junction 
  of 
  the 
  rivers 
  of 
  Ardeche 
  and 
  

   Fontaulier, 
  is 
  the 
  picturesque 
  Castle 
  of 
  Mayras, 
  which, 
  however, 
  offers 
  in 
  itself 
  

   nothing 
  of 
  much 
  interest. 
  Opposite 
  to 
  this 
  castle 
  (on 
  the 
  other 
  side 
  of 
  the 
  

   Ardeche) 
  the 
  lava 
  cliff 
  continues 
  from 
  the 
  point 
  already 
  described, 
  so 
  that 
  the 
  

   colonnade 
  of 
  La 
  Beaume 
  owes 
  its 
  origin 
  to 
  the 
  western, 
  and 
  not 
  to 
  the 
  eastern 
  

   valleys 
  which 
  unite 
  there. 
  There 
  is 
  little 
  doubt, 
  however, 
  that 
  the 
  lava 
  stream 
  

   of 
  the 
  eastern 
  valley 
  (or 
  that 
  of 
  Montpezat) 
  may 
  be 
  traced 
  at 
  the 
  sharp 
  turn 
  of 
  

   the 
  road 
  to 
  Thuez, 
  opposite 
  the 
  Chateau 
  de 
  Mayras, 
  where 
  there 
  is 
  evidently 
  an 
  

   older 
  and 
  inferior 
  stratum 
  of 
  lava 
  below 
  the 
  greater 
  colonnade. 
  A 
  section 
  at 
  this 
  

   point, 
  of 
  a 
  cliff 
  about 
  100 
  feet 
  in 
  height, 
  is 
  given 
  in 
  fig. 
  2. 
  The 
  bed 
  No. 
  3, 
  I 
  take 
  

   to 
  be 
  the 
  lava 
  of 
  the 
  valley 
  of 
  Montpezat. 
  It 
  contains 
  a 
  remarkable 
  quantity 
  of 
  

   olivine, 
  and 
  is 
  here 
  amorphous 
  : 
  it 
  is 
  completely 
  detached 
  from 
  the 
  superior 
  mass, 
  

   which 
  is 
  beautifully 
  columnar 
  where 
  it 
  rests 
  upon 
  the 
  older 
  bed, 
  the 
  columns 
  

   being 
  vertical, 
  since 
  they 
  rest 
  upon 
  a 
  horizontal 
  base. 
  The 
  beds 
  Nos. 
  1 
  and 
  2 
  

   might 
  appear 
  also 
  to 
  belong 
  to 
  distinct 
  currents, 
  the 
  upper 
  part 
  shewing 
  but 
  im- 
  

   perfect 
  columns; 
  a 
  close 
  examination 
  shews, 
  however, 
  that 
  the 
  beds 
  (1) 
  and 
  (2) 
  

   inosculate 
  in 
  such 
  a 
  manner 
  as 
  to 
  leave 
  no 
  doubt 
  of 
  their 
  being 
  due 
  to 
  one 
  and 
  

   the 
  same 
  eruption, 
  and 
  that 
  the 
  distinction 
  is 
  caused 
  by 
  the 
  accidental 
  manner 
  

   of 
  their 
  consolidation. 
  

  

  Valley 
  of 
  the 
  Alignon 
  — 
  Jaujac. 
  

  

  A 
  short 
  distance 
  higher 
  up, 
  the 
  Ardeche 
  divides 
  from 
  its 
  tributary 
  the 
  

   Alignon, 
  the 
  former 
  descending 
  from 
  Thuez, 
  the 
  latter 
  from 
  Jaujac. 
  The 
  great 
  

   mass 
  of 
  the 
  lava 
  which 
  we 
  are 
  tracing 
  evidently 
  descends 
  from 
  the 
  latter 
  valley, 
  

   and 
  here 
  we 
  gain 
  the 
  first 
  view 
  of 
  one 
  of 
  the 
  volcanic 
  vents 
  which 
  has 
  furnished 
  

   the 
  lavas 
  of 
  the 
  lower 
  valleys, 
  but 
  presents 
  from 
  this 
  point 
  no 
  trace 
  of 
  a 
  crater. 
  

   It 
  is 
  situated 
  on 
  the 
  ridge 
  separating 
  the 
  valleys 
  of 
  the 
  Ardeche 
  and 
  Alignon, 
  and 
  

   is 
  sometimes 
  called 
  the 
  Volcano 
  of 
  Neyrac, 
  from 
  a 
  village 
  of 
  the 
  former, 
  or 
  Souil- 
  

   lols, 
  from 
  one 
  of 
  the 
  latter. 
  And 
  here 
  occurs 
  an 
  interesting 
  question, 
  whether 
  

   the 
  great 
  single 
  lava-flow, 
  extending 
  to 
  the 
  Pont 
  de 
  La 
  Beaume, 
  is 
  due 
  to 
  this 
  

   volcano, 
  or 
  to 
  that 
  of 
  Jaujac, 
  higher 
  up 
  the 
  Alignon 
  ; 
  for 
  it 
  undoubtedly 
  did 
  not 
  

   come 
  from 
  the 
  valley 
  of 
  Thuez 
  (on 
  the 
  Ardeche). 
  On 
  my 
  first 
  visit 
  in 
  1839, 
  1 
  

   was 
  of 
  opinion 
  that 
  the 
  stream 
  might 
  be 
  traced 
  uninterruptedly 
  from 
  the 
  volcano 
  

   of 
  Jaujac, 
  and 
  that 
  there 
  was 
  no 
  sufficient 
  evidence 
  that 
  the 
  volcano 
  of 
  Neyrac 
  

   had 
  yielded 
  a 
  considerable 
  stream 
  into 
  the 
  valley 
  of 
  the 
  Alignon, 
  notwithstanding 
  

   the 
  presumption 
  afforded 
  by 
  its 
  crater 
  (a 
  considerably 
  decayed 
  one) 
  being 
  broken 
  

  

  