﻿332 
  

  

  G. 
  ATTWOOD 
  ON 
  THE 
  GEOLOGY 
  

  

  Yig. 
  4. 
  — 
  Sketch 
  of 
  Augite-Andesite 
  with 
  Country 
  Rock 
  adhering 
  to 
  it, 
  

   from 
  the 
  surface 
  near 
  the 
  San 
  Rafael 
  tunnel 
  in 
  the 
  Aguacate 
  

   Mountains. 
  

  

  of 
  coal 
  have 
  been 
  discovered. 
  The 
  coal 
  is 
  in 
  three 
  conditions 
  : 
  — 
  one, 
  

   in 
  which 
  the 
  coal 
  is 
  compact, 
  and 
  in 
  which 
  there 
  is 
  little 
  trace 
  of 
  

   vegetable 
  structure 
  ; 
  another, 
  in 
  which 
  the 
  plants 
  are 
  partially 
  

   carbonized; 
  and 
  a 
  third, 
  which 
  shows 
  the 
  structure 
  of 
  plants 
  (pro- 
  

   bably 
  dicotyledonous). 
  The 
  coals 
  may 
  be 
  called 
  lignites 
  ; 
  they 
  are 
  

   highly 
  pyritized, 
  and 
  contain 
  in 
  many 
  places 
  beautiful 
  white 
  crys- 
  

   tals 
  of 
  melanterite, 
  also 
  pieces 
  of 
  jet. 
  

  

  Near 
  the 
  coal, 
  and 
  often 
  adhering 
  to 
  it, 
  are 
  found 
  bands 
  of 
  horn- 
  

   stone 
  or 
  chert, 
  of 
  a 
  yellowish-brown 
  colour. 
  

  

  The 
  coal-deposits 
  have 
  not 
  been 
  explored 
  thoroughly, 
  and 
  but 
  

   little 
  is 
  known 
  at 
  the 
  present 
  time 
  about 
  their 
  extent. 
  From 
  a 
  

   knowledge 
  of 
  the 
  contour 
  of 
  the 
  country 
  and 
  of 
  the 
  surrounding 
  

   rocks, 
  I 
  consider 
  it 
  probable 
  that 
  the 
  coal-deposits 
  extend 
  over 
  a 
  

   limitod 
  area 
  only. 
  

  

  We 
  now 
  come 
  to 
  a 
  series 
  of 
  ancient 
  lakes, 
  now 
  valleys, 
  whose 
  

   waters 
  have 
  been 
  tapped 
  by 
  the 
  Rio 
  Grande, 
  on 
  the 
  Pacific 
  slope, 
  

   and 
  by 
  the 
  Rio 
  Reventazon 
  on 
  the 
  Atlantic 
  slope 
  (fig. 
  5). 
  The 
  old 
  

   water-lines 
  on 
  the 
  mountain-sides, 
  and 
  on 
  the 
  hills, 
  once 
  small 
  islands, 
  

   in 
  the 
  valleys 
  of 
  Alajuela, 
  San 
  Jose, 
  and 
  Cartago, 
  are 
  very 
  marked 
  

   and 
  distinct. 
  

  

  The 
  country 
  rock 
  is 
  the 
  same 
  as 
  above, 
  and 
  continues 
  to 
  within 
  a 
  

   few 
  miles 
  of 
  Cartago. 
  Augite-andesite 
  boulders 
  are 
  found 
  on 
  both 
  

   sides 
  of 
  the 
  dividing 
  ridge 
  ; 
  and 
  in 
  the 
  valleys 
  of 
  San 
  Jose 
  and 
  

   Cartago 
  boulders 
  of 
  trachytic 
  rocks 
  are 
  met 
  with. 
  

  

  Large 
  deposits 
  of 
  a 
  fine-grained 
  soft 
  stone 
  are 
  found 
  collected 
  in 
  

   some 
  of 
  the 
  ravines 
  near 
  San 
  Jose 
  and 
  Cartago, 
  having 
  a 
  general 
  

   white 
  ground, 
  but 
  tinged 
  with 
  yellow, 
  red, 
  and 
  magenta, 
  in 
  fantastic 
  

   forms. 
  This 
  was 
  found 
  to 
  be 
  a 
  silicate 
  of 
  alumina 
  highly 
  im- 
  

   pregnated 
  with 
  iron 
  oxides; 
  in 
  places 
  the 
  stones 
  are 
  kaolinized, 
  

   and 
  resemble 
  lithomarge. 
  

  

  Near 
  this 
  latter 
  rock 
  are 
  found, 
  more 
  or 
  less 
  connected 
  with 
  it, 
  

   masses 
  of 
  hard 
  white 
  porcelain-clay, 
  resembling 
  kaolin, 
  or 
  even 
  

   lithomarge. 
  

  

  