﻿OF 
  A 
  PAKT 
  OP 
  COSTA 
  RICA. 
  

  

  333 
  

  

  A 
  few 
  miles 
  to 
  the 
  west 
  of 
  

   Cartago, 
  and 
  near 
  the 
  base 
  of 
  the 
  

   •volcano 
  Irazu, 
  the 
  usual 
  country 
  

   rock 
  is 
  hidden 
  from 
  view, 
  and 
  

   replaced 
  by 
  a 
  greyish 
  - 
  looking 
  

   rock, 
  which 
  is 
  coarsely 
  crystalline 
  

   and 
  rough, 
  and 
  unpleasant 
  to 
  

   handle, 
  and 
  in 
  which 
  the 
  felspathic 
  

   crystals 
  predominate 
  (No. 
  5 
  in 
  

   the 
  Appendix, 
  p. 
  338, 
  is 
  a 
  variety 
  

   of 
  this 
  rock). 
  

  

  The 
  felspars 
  are 
  chiefly 
  oligo- 
  

   clase; 
  and 
  both 
  grains 
  and 
  crystals 
  

   of 
  quartz 
  were 
  observed, 
  also 
  a 
  

   little 
  sanidine, 
  augite, 
  magnetite, 
  

   and 
  some 
  iron 
  oxides. 
  The 
  rock 
  

   is 
  a 
  trachyte, 
  and 
  most 
  probably 
  

   a 
  quartz-trachyte. 
  It 
  is 
  known 
  

   in 
  the 
  country 
  as 
  the 
  " 
  Cartago 
  

   Stone," 
  owing 
  to 
  many 
  of 
  the 
  

   churches 
  and 
  public 
  buildings 
  

   being 
  constructed 
  of 
  it. 
  

  

  In 
  the 
  several 
  ravines 
  to 
  the 
  

   south-east 
  of 
  the 
  volcanoes 
  Irazu 
  

   and 
  Turrialba, 
  deposits 
  of 
  sand- 
  

   stone 
  are 
  found, 
  containing 
  slight 
  

   traces 
  of 
  decomposed 
  felspar. 
  

  

  In 
  ravines 
  and 
  on 
  the 
  moun- 
  

   tain-slopes 
  of 
  the 
  volcanoes 
  Irazu 
  

   and 
  Turrialba 
  a 
  trachytic 
  rock 
  is 
  

   frequently 
  found 
  much 
  finer-grain- 
  

   ed 
  than 
  the 
  "Cartago" 
  rock, 
  but 
  

   containing 
  less 
  quartz 
  than 
  the 
  

   coarser 
  crystalline 
  variety. 
  It 
  is 
  

   probably 
  a 
  quartz-trachyte. 
  

  

  Amongst 
  the 
  large 
  boulders 
  of 
  

   trachytic 
  rock 
  which 
  lie 
  scattered 
  

   on 
  the 
  hill 
  and 
  slopes 
  above 
  the 
  

   town 
  of 
  Cartago 
  numerous 
  volcanic 
  

   nodules 
  were 
  observed, 
  very 
  close- 
  

   grained, 
  and 
  of 
  greyish 
  colour, 
  

   with 
  specks 
  of 
  visible 
  augite. 
  

   Mr. 
  Hudleston 
  describes 
  it 
  as 
  a 
  fel- 
  

   spathic 
  tuff, 
  largely 
  made 
  up 
  of 
  

   soda 
  felspars 
  (Appendix, 
  No. 
  7, 
  

   p. 
  339). 
  Several 
  nodules 
  were 
  

   observed 
  about 
  4-1- 
  feet 
  in 
  diameter. 
  

   They 
  are 
  evidently 
  ejectamenta 
  

   from 
  either 
  Irazu 
  or 
  Turrialba. 
  

  

  

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