﻿MONTPEZAT 
  — 
  LAVA 
  OF 
  CHAMBON. 
  25 
  

  

  volcanic 
  products, 
  fills 
  the 
  bed 
  of 
  the 
  stream 
  for 
  a 
  very 
  considerable 
  distance, 
  

   rising 
  with 
  a 
  very 
  steep 
  acclivity, 
  which 
  shews 
  that 
  its 
  viscidity 
  must 
  have 
  been 
  

   considerable 
  to 
  allow 
  it 
  to 
  harden 
  at 
  so 
  great 
  an 
  inclination. 
  M. 
  Serrouil, 
  watch- 
  

   maker 
  at 
  Montpezat, 
  showed 
  me 
  a 
  sapphire 
  and 
  zircon 
  which 
  he 
  had 
  picked 
  up 
  

   near 
  this 
  place, 
  which 
  is 
  interesting 
  from 
  the 
  occurrence 
  of 
  these 
  minerals 
  in 
  the 
  

   lavas 
  of 
  Croustet, 
  near 
  Le 
  Puy. 
  The 
  lava 
  of 
  Le 
  Fau 
  is 
  surmounted 
  by 
  beds 
  of 
  

   volcanic 
  conglomerate, 
  of 
  which 
  the 
  river 
  has 
  made 
  a 
  section 
  in 
  passing 
  between 
  

   it 
  and 
  the 
  granite 
  on 
  the 
  right 
  bank 
  of 
  the 
  valley 
  ; 
  the 
  thickness 
  of 
  the 
  conglome- 
  

   rate 
  is 
  here 
  at 
  least 
  100 
  feet, 
  and 
  the 
  inclination 
  may 
  amount 
  to 
  25°. 
  The 
  vol- 
  

   canic 
  stream 
  presents 
  a 
  very 
  massive 
  and 
  striking 
  appearance, 
  and 
  leads 
  to 
  the 
  

   belief 
  that 
  we 
  are 
  in 
  the 
  immediate 
  neighbourhood 
  of 
  a 
  volcanic 
  focus 
  ; 
  and 
  such 
  

   might 
  be 
  supposed 
  to 
  exist 
  in 
  the 
  steep 
  slopes 
  covered 
  with 
  slag 
  and 
  volcanic 
  con- 
  

   glomerate 
  (the 
  conglomerate 
  still 
  uppermost), 
  which 
  rise 
  to 
  a 
  great 
  height 
  on 
  the 
  

   left 
  bank 
  of 
  the 
  stream, 
  not 
  far 
  from 
  its 
  source. 
  Nothing 
  of 
  the 
  kind, 
  however, 
  

   appears 
  ; 
  the 
  beds 
  become 
  thinner, 
  and 
  are 
  in 
  absolute 
  contact 
  at 
  no 
  great 
  depth 
  

   with 
  the 
  granite 
  which 
  constitutes 
  the 
  neighbouring 
  slopes, 
  or 
  with 
  granitic 
  bould- 
  

   ers 
  covering 
  the 
  rock 
  at 
  D, 
  Plate 
  IV., 
  fig. 
  2. 
  The 
  lava 
  in 
  contact 
  with 
  the 
  granite 
  

   has 
  evidently 
  consolidated 
  in 
  its 
  present 
  position, 
  from 
  the 
  nicety 
  of 
  its 
  adaptation 
  

   to 
  the 
  rock, 
  and 
  from 
  the 
  shortness 
  and 
  fragility 
  of 
  its 
  structure. 
  The 
  position 
  of 
  

   this 
  volcanic 
  curtain 
  will 
  be 
  best 
  understood 
  from 
  the 
  plan 
  in 
  the 
  figure 
  just 
  re- 
  

   ferred 
  to, 
  which 
  shews 
  the 
  uppermost 
  part 
  of 
  the 
  valley 
  of 
  Montpezat, 
  as 
  traversed 
  

   by 
  the 
  very 
  steep 
  paved 
  road 
  leading 
  by 
  the 
  hamlet 
  of 
  Le 
  Pal 
  from 
  Usclades 
  and 
  Le 
  

   Puy. 
  This 
  road 
  has 
  since 
  been 
  superseded 
  by 
  a 
  new 
  one, 
  which 
  was 
  nearly 
  com- 
  

   pleted 
  at 
  the 
  time 
  of 
  my 
  last 
  visit. 
  It 
  will 
  be 
  seen 
  that 
  the 
  highly-inclined 
  beds 
  

   D, 
  are 
  those 
  now 
  described, 
  and 
  are 
  divided 
  by 
  a 
  streamlet 
  which 
  issues 
  from 
  a 
  

   kind 
  little 
  circular 
  valley, 
  in 
  which 
  a 
  cottage 
  is 
  marked.* 
  This 
  circus 
  might 
  well 
  

   pass, 
  upon 
  a 
  superficial 
  examination, 
  for 
  the 
  source 
  of 
  the 
  lava 
  or 
  a 
  true 
  crater. 
  

   It 
  has, 
  however, 
  no 
  such 
  pretension, 
  being 
  completely 
  excavated 
  in 
  granite 
  ; 
  and 
  

   the 
  aforesaid 
  curtain 
  of 
  lava 
  and 
  breccia 
  forming 
  a 
  thin 
  exterior 
  facing 
  on 
  the 
  side 
  

   exposed 
  to 
  the 
  high 
  road. 
  The 
  height 
  which 
  the 
  volcanic 
  formations 
  attain 
  on 
  

   this 
  slope 
  is 
  no 
  less 
  than 
  4134 
  feet 
  above 
  the 
  sea, 
  and 
  nearly 
  2300 
  feet 
  above 
  

   Montpezat, 
  though 
  so 
  little 
  distant. 
  It 
  will 
  be 
  understood, 
  therefore, 
  that 
  the 
  

   slope 
  is 
  extremely 
  rapid. 
  

  

  The 
  place 
  where 
  these 
  remains 
  occur 
  is 
  called 
  Le 
  Chambon 
  : 
  we 
  shall 
  there- 
  

   fore 
  denominate 
  the 
  deposit 
  by 
  the 
  name 
  of 
  the 
  lava 
  of 
  Chambon. 
  It 
  is 
  hoped 
  

   that 
  it 
  has 
  been 
  made 
  evident 
  that 
  no 
  eruption 
  took 
  place 
  in 
  this 
  spot. 
  The 
  ex- 
  

   cavation 
  of 
  the 
  ravine 
  behind 
  D, 
  and 
  the 
  numerous 
  contacts 
  with 
  the 
  granitic 
  soil, 
  

   shew 
  that 
  it 
  is 
  entirely 
  foreign 
  to 
  the 
  place. 
  Whence 
  then 
  is 
  it 
  derived 
  ? 
  There 
  

   can 
  be 
  but 
  one 
  answer, 
  even 
  although 
  that 
  conclusion 
  be 
  attended 
  with 
  some 
  diffi- 
  

  

  * 
  There 
  is 
  also 
  another 
  cottage 
  more 
  to 
  the 
  left, 
  in 
  a 
  place 
  where, 
  on 
  Cassini's 
  Map, 
  is 
  marked 
  

   " 
  Lac 
  de 
  Ferrand 
  ;" 
  that 
  little 
  lake 
  in 
  reality 
  lying 
  higher 
  up 
  in 
  the 
  direction 
  of 
  the 
  volcano 
  of 
  

   Bauzon. 
  

  

  VOL. 
  XX. 
  PART 
  I. 
  G 
  

  

  