﻿MONTPEZAT 
  — 
  VALLEY 
  OF 
  THE 
  FONTAULIER. 
  23 
  

  

  pezat 
  and 
  Burzet. 
  It 
  is 
  a 
  real 
  cup 
  — 
  the 
  bottom 
  being- 
  lower 
  than 
  the 
  lowest 
  edge 
  

   of 
  the 
  crater 
  by 
  which 
  the 
  lava 
  has 
  poured 
  out 
  into 
  the 
  valley. 
  A 
  high 
  and 
  

   solid 
  conoidal 
  mass 
  of 
  lava 
  and 
  ashes 
  commands 
  the 
  crater 
  to 
  the 
  SW. 
  so 
  as 
  to 
  

   give 
  the 
  character 
  of 
  an 
  unbroken 
  top 
  to 
  the 
  hill 
  in 
  that 
  direction. 
  The 
  highest 
  

   parts 
  are 
  composed 
  of 
  partly 
  solid 
  lava, 
  and 
  rise 
  100 
  feet 
  above 
  the 
  bottom 
  of 
  the 
  

   crater* 
  The 
  principal 
  lava-flow 
  descends 
  in 
  the 
  direction 
  of 
  Montpezat, 
  at 
  an 
  angle 
  

   (by 
  estimation) 
  of 
  little 
  less 
  than 
  35 
  J 
  ; 
  yet 
  it 
  is 
  tolerably 
  continuous. 
  At 
  its 
  base, 
  

   near 
  the 
  bridge 
  across 
  the 
  Fontaulier 
  (which 
  is 
  1534 
  feet 
  above 
  the 
  sea, 
  and 
  1200 
  

   below 
  the 
  summit 
  of 
  the 
  Gravenne), 
  we 
  have 
  a 
  remarkable 
  section, 
  Plate 
  III., 
  fig. 
  

   5, 
  which 
  is 
  made 
  transversely 
  to 
  the 
  direction 
  of 
  the 
  lava 
  stream 
  of 
  the 
  Gravenne, 
  

   which 
  forms 
  the 
  upper 
  layer. 
  The 
  layer 
  of 
  basalt 
  forming 
  the 
  base 
  of 
  the 
  section, 
  

   and 
  which 
  is 
  separated 
  from 
  the 
  other 
  by 
  a 
  layer 
  of 
  granite 
  boulders, 
  cemented 
  

   like 
  that 
  of 
  Neyrac 
  by 
  the 
  action 
  of 
  the 
  acidulous 
  water, 
  is 
  evidently 
  the 
  product 
  

   of 
  an 
  altogether 
  anterior 
  eruption. 
  The 
  more 
  modern 
  eruption 
  has 
  bathed 
  the 
  

   whole 
  valley 
  with 
  lava, 
  which 
  has 
  formed 
  a 
  tolerably 
  level 
  prismatic 
  bed, 
  stretch- 
  

   ing 
  some 
  way 
  up 
  the 
  tributary 
  stream 
  of 
  the 
  Pourseuille, 
  as 
  well 
  as 
  up 
  the 
  

   valley 
  of 
  the 
  Fontaulier, 
  but 
  not 
  far 
  in 
  either 
  case, 
  and 
  stopping 
  considerably 
  

   short 
  of 
  the 
  town 
  or 
  village 
  of 
  Montpezat, 
  which 
  is 
  built 
  upon 
  a 
  mass 
  of 
  granite 
  

   boulders. 
  The 
  junction 
  of 
  the 
  Pourseuille 
  and 
  Fontaulier 
  affords 
  an 
  excellent 
  

   section 
  below 
  the 
  picturesque 
  site 
  of 
  the 
  Castle 
  of 
  Pourchirol, 
  Plate 
  III., 
  fig. 
  6. 
  

   Here 
  but 
  one 
  bed 
  of 
  basalt 
  appears 
  (I 
  mean 
  due 
  to 
  one 
  eruption). 
  

  

  The 
  plateau 
  formed 
  in 
  the 
  valley 
  of 
  the 
  Fontaulier 
  by 
  the 
  lava 
  of 
  the 
  Gra- 
  

   venne 
  is 
  justly 
  described 
  by 
  Mr 
  Scrope 
  as 
  having 
  " 
  its 
  upper 
  surface 
  bristled 
  

   with 
  rocky 
  and 
  scoriform 
  projections; 
  which, 
  however, 
  by 
  decomposition, 
  resolve 
  

   themselves 
  into 
  a 
  rich 
  soil, 
  affording 
  nourishment 
  to 
  very 
  productive 
  chestnut 
  

   forests." 
  Many 
  scenes 
  of 
  great 
  beauty 
  occur 
  on 
  this 
  plateau. 
  There 
  is 
  some 
  

   appearance 
  of 
  a 
  lake 
  having 
  been 
  formed 
  at 
  the 
  contraction 
  of 
  the 
  valley 
  at 
  the 
  

   Pont 
  de 
  la 
  Motte, 
  several 
  miles 
  farther 
  down 
  ; 
  and 
  both 
  in 
  this 
  valley 
  and 
  that 
  of 
  

   Burzet 
  (which 
  we 
  shall 
  afterwards 
  describe) 
  there 
  occur 
  deposits 
  of 
  pozzuolana 
  

   apparently 
  stratified 
  by 
  water. 
  At 
  the 
  junction 
  of 
  the 
  Fontaulier 
  with 
  the 
  tri- 
  

   butary 
  valley 
  of 
  Burzet, 
  about 
  half-way 
  between 
  the 
  Gravenne 
  and 
  the 
  Pont 
  de 
  

   la 
  Beaume, 
  the 
  lava 
  of 
  Montpezat 
  joins 
  that 
  of 
  Burzet, 
  or 
  rather, 
  overlies 
  it, 
  — 
  the 
  

   plan 
  and 
  section, 
  Plate 
  IV., 
  fig. 
  1, 
  marking 
  plainly 
  the 
  more 
  recent 
  date 
  of 
  the 
  

   eruption 
  of 
  the 
  Gravenne. 
  These 
  streams 
  remain 
  superposed 
  for 
  some 
  distance 
  ; 
  

   but 
  at 
  the 
  Pont 
  de 
  la 
  Motte 
  (at 
  Mayras) 
  there 
  is 
  only 
  a 
  single 
  stream, 
  which 
  is 
  

   columnar, 
  abounds 
  in 
  olivine, 
  and 
  reposes 
  on 
  a 
  conglomerate, 
  I 
  am 
  unable 
  to 
  state 
  

   positively 
  to 
  which 
  of 
  the 
  two 
  valleys 
  this 
  may 
  be 
  traced 
  (although 
  the 
  determi- 
  

   nation 
  would 
  be 
  easy) 
  ; 
  but 
  from 
  its 
  composition 
  and 
  other 
  circumstances, 
  I 
  am 
  

   inclined 
  to 
  think 
  that 
  it 
  derived 
  from 
  the 
  valley 
  of 
  Burzet. 
  It 
  continues 
  all 
  the 
  

  

  * 
  Messrs 
  Lyell 
  & 
  Murchison 
  (Edin. 
  Phil. 
  Journal, 
  1829, 
  p. 
  27) 
  speak 
  of 
  angular 
  blocks 
  

   of 
  unaltered 
  gneiss 
  as 
  occurring 
  near 
  the 
  summit 
  of 
  the 
  Gravenne. 
  These 
  appear 
  to 
  have 
  escaped 
  

   my 
  notice. 
  

  

  