﻿ACADEMY 
  OF 
  SCIENCES. 
  213 
  

  

  tlie 
  (lecomposod 
  rock 
  is 
  Vjlowii 
  away 
  as 
  fast 
  as 
  it 
  is 
  forrnod. 
  As 
  well 
  as 
  I 
  could 
  

   judge, 
  I 
  think 
  there 
  must 
  liave 
  been 
  more 
  than 
  a 
  hundred 
  of 
  these 
  different 
  

   eruptions. 
  The 
  beds 
  vary 
  much 
  in 
  thickness, 
  some 
  being 
  not 
  more 
  than 
  two 
  

   or 
  three 
  feet 
  thick, 
  whilst 
  other 
  present 
  escarpments 
  fifty 
  feet 
  high. 
  As 
  

   will 
  be 
  seen 
  from 
  the 
  ppecimens 
  I 
  have 
  placed 
  on 
  the 
  table, 
  these 
  rocks 
  

   differ 
  much 
  in 
  their 
  appearance, 
  although, 
  for 
  the 
  reasons 
  before 
  stated, 
  

   specimens 
  of 
  the 
  harder 
  rocks 
  were 
  mostly 
  obtained. 
  The 
  specimens 
  num- 
  

   bered 
  from 
  one 
  to 
  six 
  (see 
  woodcut) 
  were 
  collected 
  in 
  about 
  a 
  space 
  of 
  

   400 
  yards, 
  towards 
  the 
  foot 
  of 
  the 
  mountain 
  ; 
  from 
  seven 
  to 
  eleven, 
  about 
  

   half 
  way 
  up 
  ; 
  and 
  from 
  twelve 
  to 
  fifteen, 
  within 
  100 
  yards 
  of 
  the 
  sum- 
  

   mit. 
  As 
  will 
  be 
  seen, 
  the 
  rocks 
  present 
  many 
  varieties, 
  the 
  greater 
  number, 
  

   however, 
  resembling 
  anamesite. 
  The 
  true 
  basalts 
  were 
  not 
  often 
  found 
  

   on 
  the 
  surface, 
  as 
  they 
  were 
  generally 
  so 
  decomposed 
  that 
  the 
  position 
  

   they 
  occupied 
  was 
  only 
  indicated 
  by 
  the 
  surface 
  being 
  covered 
  with 
  bright 
  

   red 
  dust, 
  containing 
  a 
  large 
  quantity 
  of 
  zeolites. 
  Interatratified 
  with 
  these 
  

   basaltic 
  rocks, 
  we 
  find 
  beds 
  of 
  diabase 
  and 
  labrador 
  porphyry, 
  and 
  towards 
  the 
  

   top 
  we 
  find 
  vesicular 
  trachyte 
  and 
  porphyritic 
  obsidian. 
  These 
  beds 
  seem 
  to 
  

   follow 
  no 
  regular 
  order 
  : 
  for 
  instance, 
  between 
  two 
  beds 
  of 
  anamesite 
  is 
  a 
  bed 
  

   of 
  diabase. 
  The 
  labrador 
  porphyry 
  is 
  in 
  contact 
  with 
  true 
  basalt, 
  and 
  imme- 
  

   diately 
  above 
  the 
  vesicular 
  trachyte, 
  is 
  a 
  bed 
  of 
  anamesite, 
  forming 
  the 
  crest 
  of 
  

   the 
  ridge 
  ; 
  below 
  it, 
  is 
  a 
  bed 
  of 
  porphyritic 
  obsidian 
  ; 
  then, 
  apparently 
  for 
  

   some 
  distance, 
  a 
  bed 
  of 
  true 
  basalt, 
  the 
  surface 
  being 
  covered 
  with 
  red 
  dust, 
  

   mixed 
  with 
  a 
  large 
  quantity 
  of 
  zeolites 
  ; 
  and 
  cropping 
  out 
  below 
  this, 
  is 
  another 
  

   bed 
  of 
  anamesite. 
  There 
  is 
  a 
  general 
  mineralogical 
  resemblance 
  between 
  the 
  

   (lifTerent 
  beds, 
  with 
  the 
  exception 
  of 
  the 
  true 
  basalts 
  and 
  the 
  trachytic 
  rocks. 
  

   The 
  others 
  are 
  composed 
  almost 
  entirely 
  of 
  labrador 
  and 
  augite, 
  in 
  varying 
  pro- 
  

   portions, 
  and 
  contained 
  under 
  different 
  forms 
  in 
  the 
  different 
  varieties 
  of 
  rocks, 
  

   the 
  labrador 
  being 
  sometimes 
  in 
  large 
  twin 
  crystals, 
  and 
  in 
  other 
  rocks 
  forming 
  

   a 
  complete 
  network 
  of 
  minute 
  crystals, 
  which 
  so 
  thoroughly 
  pervade 
  the 
  rocks 
  

   as 
  to 
  prevent 
  any 
  other 
  form 
  of 
  crystal 
  being 
  made 
  out, 
  although 
  the 
  presence 
  

   of 
  augite 
  is 
  rendered 
  almost 
  certain 
  by 
  polarised 
  light. 
  In 
  the 
  labrador 
  por- 
  

   phyry, 
  the 
  crystals 
  of 
  labrador 
  are 
  sometimes 
  an 
  inch 
  long. 
  The 
  augite 
  is 
  

   sometimes 
  in 
  grains, 
  but 
  more 
  frequently 
  in 
  crystalline 
  plates 
  ; 
  it 
  is 
  usually 
  

   green 
  or 
  brown. 
  Magnetic 
  oxide 
  of 
  iron 
  is 
  present 
  in 
  most 
  of^ 
  the 
  rocks, 
  

   although 
  not 
  in 
  any 
  largo 
  quantity, 
  except 
  in 
  the 
  true 
  basalts, 
  and 
  in 
  some 
  of 
  

   the 
  darker 
  anamesites. 
  Sanadine 
  has 
  been 
  found 
  in 
  the 
  trachytes 
  and 
  in 
  the 
  

   basalts. 
  Olivine, 
  as 
  usual, 
  is 
  met 
  with 
  in 
  the 
  basalts, 
  and 
  in 
  most 
  of 
  the 
  rocks 
  

   micro-crystals 
  are 
  met 
  with 
  in 
  large 
  quantities. 
  In 
  general, 
  the 
  rocks 
  are 
  so 
  

   completely 
  formed 
  of 
  crystalline 
  elements, 
  that 
  vitreous 
  matter 
  exists 
  in 
  but 
  

   small 
  quantities; 
  it 
  is 
  generally 
  pellucid 
  and 
  colorless, 
  but 
  in 
  some 
  instances 
  

   green. 
  On 
  account 
  of 
  the 
  only 
  specimens 
  obtainable 
  being 
  generally 
  so 
  much 
  

   weathered, 
  the 
  exact 
  determination 
  of 
  their 
  crystalline 
  structure 
  was 
  difficult. 
  

   The 
  chemical 
  composition 
  of 
  some 
  of 
  these 
  rocks 
  has 
  been 
  determined, 
  and 
  

   furnishes 
  quantities 
  of 
  the 
  diff.'rent 
  substances 
  of 
  which 
  they 
  are 
  composed, 
  

   which 
  vary 
  considerably 
  in 
  the 
  different 
  specimens 
  ; 
  for 
  instance, 
  in 
  the 
  red 
  

  

  