﻿PECULIAR 
  VOLCANIC 
  PHENOMENA 
  OF 
  PAL 
  AND 
  CHAMBON. 
  27 
  

  

  thousand 
  cases 
  of 
  excavation 
  which 
  most 
  hilly 
  countries 
  exhibit, 
  but 
  of 
  which 
  no 
  

   geological 
  hypothesis 
  has 
  yet 
  given 
  any 
  satisfactory 
  account. 
  In 
  this 
  case, 
  the 
  diffi- 
  

   culty 
  of 
  the 
  explanation 
  is 
  increased 
  by 
  the 
  circumstance, 
  that 
  the 
  excavation 
  has 
  

   occurred 
  since 
  the 
  deposition 
  of 
  a 
  very 
  recent 
  lava, 
  a 
  lava 
  which 
  has 
  itself 
  covered 
  

   the 
  boulders 
  due 
  to 
  a 
  previous 
  denudation. 
  

  

  I 
  need 
  hardly 
  say 
  one 
  word 
  of 
  M. 
  Burat's 
  assertion, 
  that 
  the 
  lava 
  of 
  Cham- 
  

   bon 
  is 
  an 
  " 
  epanchement 
  lateral 
  " 
  from 
  the 
  granite 
  wall 
  of 
  the 
  crater 
  of 
  Pal 
  ; 
  in 
  other 
  

   words, 
  that 
  it 
  has 
  issued 
  by 
  a 
  subterranean 
  orifice 
  from 
  the 
  same 
  internal 
  focus. 
  

   Such 
  an 
  explanation 
  would 
  be 
  highly 
  satisfactory 
  were 
  it 
  founded 
  on 
  fact. 
  But 
  

   we 
  have 
  seen 
  that 
  no 
  such 
  orifice 
  exists. 
  Did 
  it 
  exist, 
  it 
  must 
  be 
  at 
  a 
  higher 
  level 
  

   than 
  the 
  highest 
  point 
  of 
  the 
  volcanic 
  accumulations 
  D 
  (fig. 
  2) 
  ; 
  but 
  the 
  lava 
  has 
  

   there 
  only 
  a 
  few 
  feet 
  of 
  thickness, 
  and 
  beyond, 
  above, 
  and 
  around 
  it, 
  the 
  bare 
  

   granite 
  is 
  everywhere 
  exposed, 
  the 
  circus 
  extending 
  from 
  E 
  to 
  D, 
  being 
  through- 
  

   out 
  entire, 
  generally 
  precipitous, 
  and 
  presenting 
  no 
  fissure. 
  To 
  this 
  may 
  be 
  added 
  

   the 
  fact, 
  that 
  the 
  highest 
  part 
  of 
  D 
  is 
  higher 
  than 
  the 
  present 
  level 
  of 
  the 
  interior 
  

   surface 
  of 
  the 
  crater 
  of 
  Pal, 
  as 
  the 
  following 
  barometrical 
  heights 
  attest. 
  

  

  1839, 
  June 
  3. 
  — 
  Lowest 
  part 
  of 
  Crater 
  of 
  Pal, 
  

  

  Highest 
  Boundary 
  of 
  the 
  Crater 
  to 
  NE. 
  (con- 
  

   glomerate), 
  ..... 
  

   Highest 
  point 
  Lava 
  of 
  Chambon, 
  

  

  The 
  whole 
  relations 
  of 
  this 
  singular 
  formation 
  will, 
  I 
  hope, 
  be 
  made 
  plainer 
  

   by 
  the 
  elevation, 
  or 
  distant 
  perspective 
  view 
  in 
  Plate 
  IV., 
  fig. 
  3, 
  carefully 
  drawn 
  

   from 
  the 
  top 
  of 
  the 
  Gravenne 
  of 
  Montpezat. 
  The 
  same 
  letters 
  of 
  reference 
  are 
  

   used 
  as 
  far 
  as 
  possible 
  in 
  figs. 
  2 
  and 
  3. 
  

  

  The 
  crater 
  of 
  Le 
  Pal 
  has 
  acquired 
  some 
  celebrity 
  by 
  the 
  discussions 
  to 
  which 
  

   it 
  has 
  given 
  rise 
  in 
  the 
  Geological 
  Society 
  of 
  France;* 
  having 
  been 
  by 
  some 
  

   regarded 
  as 
  the 
  type 
  of 
  a 
  crater 
  of 
  elevation, 
  as 
  composed 
  entirely 
  of 
  granitic 
  

   strata 
  elevated 
  so 
  as 
  to 
  present 
  a 
  volcano 
  composed 
  of 
  primitive 
  rock. 
  I 
  cannot 
  

   at 
  all 
  partake 
  of 
  this 
  view 
  ; 
  and 
  indeed 
  can 
  affirm, 
  from 
  the 
  most 
  careful 
  and 
  re- 
  

   peated 
  examination, 
  that 
  it 
  presents 
  no 
  peculiarity 
  which 
  can 
  cause 
  it 
  to 
  be 
  con- 
  

   sidered 
  as 
  exceptional, 
  unless 
  the 
  insignificant 
  quantity 
  of 
  scoriae 
  ejected 
  by 
  it 
  

   (or, 
  at 
  least, 
  which 
  are 
  now 
  visible), 
  which 
  is 
  insufficient 
  to 
  form 
  a 
  true 
  

   cone 
  like 
  that 
  of 
  the 
  neighbouring 
  volcano 
  of 
  Bauzon. 
  The 
  primitive 
  rocks 
  

   appeared 
  to 
  me 
  here 
  as 
  elsewhere 
  to 
  be 
  undisturbed 
  ; 
  — 
  to 
  have 
  no 
  exterior 
  

   configuration 
  whatever, 
  indicating 
  that 
  they 
  have 
  been 
  moulded 
  by 
  the 
  pres- 
  

   sure 
  of 
  lava 
  in 
  the 
  interior 
  ; 
  and 
  certainly 
  not 
  to 
  possess 
  the 
  character 
  of 
  " 
  in- 
  

   ternal 
  precipices 
  (forming 
  the 
  crater) 
  with 
  gentle 
  external 
  slopes 
  : 
  " 
  the 
  section 
  

   in 
  fig. 
  2 
  shews 
  just 
  the 
  reverse. 
  In 
  fact, 
  the 
  granitic 
  eminences 
  by 
  which 
  

   the 
  crater 
  of 
  Pal 
  is 
  partly 
  surrounded, 
  are 
  (as 
  already 
  mentioned) 
  the 
  culmina- 
  

  

  * 
  Bulletin 
  de 
  la 
  Societe 
  Geologique 
  de 
  France. 
  Tom. 
  III. 
  and 
  IV. 
  

  

  Barom. 
  mill. 
  

  

  Ht. 
  above 
  Sea. 
  

  

  661-6 
  

  

  3803 
  feet 
  

  

  646-9 
  

  

  4537 
  ... 
  

  

  656-1 
  

  

  4134 
  ... 
  

  

  