﻿OP 
  A 
  PART 
  OP 
  COSTA 
  PICA. 
  331 
  

  

  Aguacate 
  mines 
  by 
  very 
  crude 
  appliances 
  since 
  they 
  were 
  first 
  dis- 
  

   covered 
  in 
  1822 
  ; 
  and 
  the 
  value 
  may 
  be 
  estimated 
  at 
  <£1.200,000. 
  

  

  On 
  the 
  Aguacate 
  Mountains 
  volcanic 
  rock-masses 
  were 
  observed 
  on 
  

   the 
  hill-tops, 
  on 
  the 
  sides, 
  and 
  in 
  the 
  ravines. 
  They 
  have 
  a 
  general 
  

   north- 
  and- 
  south 
  direction, 
  as 
  may 
  be 
  inferred 
  from 
  their 
  strike. 
  

   In 
  the 
  mine-workings, 
  however, 
  which 
  have 
  reached 
  a 
  depth 
  of 
  400 
  

   feet 
  vertical, 
  although 
  several 
  miles 
  of 
  subterranean 
  galleries 
  were 
  

   explored, 
  no 
  evidence 
  of 
  any 
  eruptive 
  rock-masses 
  cutting 
  the 
  veins 
  

   was 
  discovered, 
  or 
  of 
  their 
  disturbing 
  the 
  same. 
  Numerous 
  galleries 
  

   which 
  have 
  been 
  run 
  outside 
  the 
  veins 
  prove, 
  in 
  many 
  cases, 
  the 
  

   existence 
  of 
  the 
  two 
  different 
  rocks 
  — 
  the 
  country 
  rock 
  (or 
  conso- 
  

   lidated 
  ash) 
  and 
  the 
  augite-andesite, 
  which 
  are 
  often 
  in 
  contact 
  

   (fig. 
  4). 
  

  

  Fig. 
  3. 
  — 
  Directions 
  of 
  Lodes 
  in 
  the 
  Aguacate 
  Mines. 
  

  

  a, 
  a'. 
  Strike 
  of 
  the 
  Oreamunos-San 
  Rafael-Los 
  Castros 
  lode, 
  N. 
  41° 
  30 
  r 
  E. 
  

  

  b, 
  V. 
  Strike 
  of 
  the 
  San 
  Miguel 
  lode, 
  N. 
  37° 
  E. 
  

  

  This 
  latter 
  rock 
  presents 
  a 
  great 
  resemblance 
  to 
  the 
  black- 
  

   looking 
  boulder-stones 
  found 
  on 
  the 
  hill-sides 
  near 
  the 
  road 
  on 
  the 
  

   way 
  from 
  Esparta 
  ; 
  and 
  the 
  result 
  of 
  a 
  microscopical 
  examination 
  

   of 
  rocks 
  found 
  near 
  the 
  surface 
  in 
  situ, 
  and 
  of 
  others 
  obtained 
  400 
  

   feet 
  below 
  the 
  surface 
  in 
  one 
  of 
  the 
  Aguacate 
  Company's 
  galleries 
  

   called 
  the 
  San 
  Eafael 
  Level 
  (Appendix, 
  No. 
  4, 
  p. 
  337), 
  prove 
  them 
  

   to 
  be 
  almost 
  identical. 
  They 
  have 
  a 
  compact 
  base, 
  are 
  of 
  a 
  brownish- 
  

   black 
  colour, 
  contain 
  triclinic 
  felspar, 
  augite, 
  magnetite, 
  specks 
  of 
  

   pyrites, 
  and 
  also 
  of 
  ferrite. 
  Petrographically 
  they 
  may 
  be 
  referred 
  

   to 
  the 
  augite-andesites, 
  and 
  occur 
  of 
  irregular 
  shape 
  and 
  size, 
  occa- 
  

   sionally 
  appearing 
  upon 
  the 
  surface, 
  but 
  often 
  hidden 
  from 
  view. 
  

   They 
  never 
  present 
  a 
  wall-like 
  mass 
  of 
  mineral 
  matter 
  filling 
  up 
  rents 
  

   or 
  fissures 
  in 
  the 
  original 
  strata. 
  

  

  A 
  sample 
  taken 
  of 
  the 
  rock 
  about 
  400 
  feet 
  below 
  the 
  surface, 
  

   and 
  near 
  the 
  point 
  of 
  contact 
  with 
  the 
  country 
  rock, 
  shows 
  slicken- 
  

   slides 
  in 
  a 
  very 
  marked 
  manner. 
  

  

  No 
  change 
  of 
  geological 
  interest 
  is 
  observed 
  until 
  the 
  river 
  called 
  

   Bio 
  Grande 
  is 
  reached. 
  In 
  several 
  ravines 
  near 
  the 
  river 
  deposits 
  

  

  