﻿VOLCANO 
  OF 
  MOULEYRES 
  — 
  ITS 
  LAVAS. 
  19 
  

  

  and 
  within 
  it, 
  that 
  we 
  are 
  to 
  look 
  for 
  the 
  source 
  of 
  the 
  great 
  eruption 
  which 
  has 
  

   at 
  one 
  time 
  levelled 
  the 
  whole 
  valley. 
  A 
  small 
  ravine 
  and 
  bridge 
  may 
  be 
  ob- 
  

   served 
  between 
  the 
  volcano 
  and 
  the 
  village. 
  This 
  is 
  called 
  the 
  Gueide 
  d'Enfer 
  by 
  

   Faujas, 
  and 
  is 
  figured 
  by 
  him 
  ; 
  the 
  Pont 
  du 
  Diable 
  is 
  concealed 
  by 
  the 
  foreground 
  

   of 
  the 
  drawing. 
  The 
  Gueule 
  d'Enfer 
  now 
  affords 
  passage 
  to 
  the 
  stream 
  belong- 
  

   ing 
  to 
  the 
  lateral 
  valley. 
  It 
  is 
  almost 
  entirely 
  formed 
  of 
  granite, 
  and 
  the 
  con- 
  

   trast 
  of 
  the 
  granite 
  and 
  basalt 
  may 
  be 
  traced 
  on 
  the 
  left 
  of 
  the 
  bridge 
  by 
  which 
  

   the 
  ascending 
  road 
  from 
  Aubenas 
  reaches 
  Thuez. 
  

  

  Now, 
  in 
  the 
  first 
  place, 
  as 
  to 
  the 
  origin 
  of 
  the 
  lava 
  there 
  can 
  be 
  no 
  doubt. 
  

   The 
  volcano 
  of 
  Mouleyres 
  or 
  Thuez 
  has 
  evidently 
  produced 
  at 
  one 
  prodigious 
  throe 
  

   all 
  this 
  mass, 
  and 
  may 
  be 
  said 
  to 
  have 
  expired 
  in 
  the 
  effort 
  ; 
  for 
  there 
  is 
  no 
  appear- 
  

   ance 
  of 
  any 
  repetition 
  of 
  the 
  action, 
  and 
  the 
  crater 
  is 
  burst 
  completely 
  open 
  on 
  

   the 
  side 
  of 
  Thuez, 
  so 
  as 
  to 
  represent, 
  like 
  many 
  volcanic 
  cones 
  near 
  Clermont, 
  the 
  

   figure 
  of 
  an 
  arm-chair. 
  A 
  portion 
  of 
  the 
  lava 
  seems, 
  however, 
  to 
  have 
  escaped 
  

   from 
  the 
  crater 
  towards 
  the 
  south, 
  and 
  to 
  have 
  formed 
  one 
  of 
  the 
  basaltic 
  plateaux 
  

   in 
  the 
  lower 
  part 
  of 
  the 
  valley, 
  and 
  at 
  a 
  much 
  lower 
  level. 
  The 
  highest 
  part 
  of 
  

   the 
  crater 
  of 
  Mouleyres 
  or 
  Thuez 
  is 
  2026 
  feet 
  above 
  the 
  sea, 
  or 
  500 
  feet 
  above 
  

   the 
  general 
  level 
  of 
  the 
  lava-bed 
  on 
  which 
  the 
  village 
  is 
  placed.* 
  

  

  We 
  shall 
  call 
  the 
  lateral 
  valley 
  of 
  Thuez 
  that 
  which 
  is 
  seen 
  in 
  the 
  pano- 
  

   ramic 
  view 
  extending 
  towards 
  the 
  Gravenne 
  of 
  Montpezat. 
  I 
  have 
  repeatedly 
  

   examined 
  the 
  whole 
  of 
  this 
  valley 
  with 
  the 
  greatest 
  care, 
  in 
  order 
  to 
  decide 
  

   whether 
  the 
  last-named 
  volcano 
  had 
  any 
  share 
  in 
  producing 
  the 
  lava 
  which 
  fills 
  

   it 
  (as 
  some 
  authors 
  have 
  supposed). 
  There 
  is 
  certainly 
  an 
  obscure 
  appearance 
  of 
  

   a 
  slaggy 
  lava-stream 
  having 
  descended 
  the 
  Gravenne 
  on 
  the 
  side 
  of 
  Thuez, 
  but 
  it 
  

   is 
  everywhere 
  covered 
  with 
  loose 
  cinders, 
  whose 
  boundary 
  with 
  the 
  granite 
  may 
  

   be 
  traced 
  right 
  and 
  left. 
  These 
  cinders 
  are 
  in 
  contact 
  with 
  the 
  slag 
  of 
  the 
  volcano 
  

   of 
  Mouleyres 
  to 
  the 
  east, 
  and 
  they 
  are 
  lost 
  in 
  the 
  bottom 
  of 
  the 
  valley 
  amongst 
  

   the 
  multitude 
  of 
  granite 
  blocks 
  by 
  which 
  it 
  is 
  entirely 
  choked, 
  and 
  through 
  which 
  

   the 
  rivulet 
  (the 
  same 
  which 
  passes 
  through 
  the 
  Gueule 
  d'Enfer) 
  makes 
  its 
  way 
  

   without 
  leaving 
  a 
  trace 
  of 
  a 
  section 
  which 
  should 
  decide 
  whether 
  or 
  not 
  there 
  is 
  

   a 
  lava-stream 
  beneath. 
  Even 
  the 
  undoubted 
  lava 
  of 
  Mouleyres 
  can 
  be 
  traced 
  but 
  

   a 
  very 
  little 
  way 
  above 
  Thuez, 
  in 
  the 
  bed 
  of 
  the 
  stream. 
  It 
  is 
  important 
  to 
  men- 
  

   tion 
  that 
  amidst 
  the 
  granite 
  blocks 
  many 
  are 
  found 
  evidently 
  altered 
  by 
  heat 
  ; 
  

   they 
  are 
  heavy, 
  red, 
  and 
  friable, 
  and 
  have 
  no 
  doubt 
  been 
  ejected 
  from 
  the 
  Gravenne. 
  

   Similar 
  blocks 
  are 
  likewise 
  common 
  at 
  Jaujac 
  and 
  elsewhere. 
  

  

  If 
  we 
  would 
  now 
  trace 
  more 
  accurately 
  the 
  composition 
  and 
  dimension 
  of 
  

   the 
  la,va-stream, 
  as 
  shewn 
  in 
  the 
  valley 
  of 
  the 
  Ardeche, 
  the 
  best 
  way 
  is 
  to 
  descend 
  

  

  * 
  The 
  elevations 
  in 
  this 
  part 
  of 
  the 
  valley 
  were 
  deduced 
  from 
  barometrical 
  observations 
  chiefly 
  

   made 
  in 
  1841, 
  and 
  referred 
  to 
  Thuez 
  as 
  a 
  standard 
  height. 
  This 
  latter 
  has 
  been 
  estimated 
  at 
  1545 
  

   feet 
  above 
  the 
  sea 
  at 
  Marseilles 
  from 
  six 
  observations 
  in 
  1839 
  and 
  1841, 
  compared 
  with 
  those 
  of 
  M. 
  

   Valz 
  at 
  Marseilles, 
  and 
  kindly 
  communicated 
  to 
  me 
  by 
  that 
  excellent 
  observer. 
  

  

  