﻿GEOLOGY. 
  43 
  

  

  less 
  purely 
  siliceous 
  varieties, 
  are 
  usually 
  full 
  of 
  small 
  brown 
  scales, 
  

   spines, 
  and 
  fragments 
  or 
  impressions 
  of 
  nondescript 
  shape 
  which 
  are 
  

   of 
  organic 
  origin 
  but 
  which 
  can 
  not 
  be 
  recognized 
  as 
  belonging 
  to 
  any 
  

   particular 
  forms. 
  Here 
  and 
  there, 
  also, 
  large 
  bones 
  are 
  embedded 
  

   in 
  the 
  deposits. 
  They 
  seem 
  to 
  be 
  those 
  of 
  whales 
  or 
  other 
  large 
  marine 
  

   vertebrates. 
  

  

  Taken 
  as 
  a 
  whole, 
  the 
  Monterey 
  shale 
  may 
  well 
  be 
  called 
  an 
  organic 
  

   formation. 
  The 
  practically 
  complete 
  absence 
  of 
  coarse 
  sediments 
  

   derived 
  from 
  erosion 
  and 
  the 
  abundance 
  of 
  fossil 
  organisms, 
  espe- 
  

   cially 
  of 
  siliceous 
  skeletons, 
  make 
  it 
  different 
  both 
  in 
  appearance 
  and 
  

   composition 
  from 
  any 
  other 
  known 
  formation 
  of 
  comparable 
  thick- 
  

   ness. 
  The 
  unaltered 
  siliceous 
  shale 
  most 
  nearly 
  resembles 
  chalk, 
  but 
  

   it 
  contains 
  only 
  a 
  small 
  proportion 
  of 
  lime. 
  Whether 
  or 
  not 
  the 
  

   organic 
  remains 
  compose 
  more 
  than 
  half 
  or 
  as 
  much 
  as 
  half 
  of 
  the 
  

   deposit 
  can 
  not 
  be 
  stated. 
  

  

  MICROSCOPIC 
  APPEARANCE. 
  

  

  Under 
  the 
  polarizing 
  microscope 
  little 
  can 
  be 
  made 
  out 
  regarding 
  

   the 
  structure 
  of 
  the 
  main 
  mass 
  of 
  the 
  soft 
  shale 
  and 
  compact 
  white 
  

   shale. 
  The 
  groundmass 
  seems 
  to 
  be 
  made 
  up 
  of 
  amorphous 
  colloidal 
  

   silica 
  surrounding 
  minute 
  grains 
  which 
  are 
  both 
  crystalline 
  and 
  amor- 
  

   phous, 
  but 
  the 
  character 
  of 
  which 
  can 
  not 
  be 
  recognized. 
  Embedded 
  

   in 
  this 
  are 
  numerous 
  imperfectly 
  angular 
  or 
  more 
  rarely 
  partially 
  

   rounded 
  crystal 
  particles, 
  probably 
  of 
  quartz. 
  Many 
  of 
  the 
  latter 
  

   look 
  as 
  if 
  they 
  were 
  due 
  to 
  secondary 
  development 
  rather 
  than 
  origi- 
  

   nating 
  as 
  clastic 
  grains. 
  

  

  In 
  the 
  more 
  flinty 
  varieties 
  the 
  rock 
  appears 
  to 
  have 
  undergone 
  par- 
  

   tial 
  and 
  local 
  crystallization 
  of 
  the 
  silica 
  throughout 
  its 
  mass. 
  In 
  the 
  

   flint, 
  in 
  which 
  there 
  are 
  alternating, 
  usually 
  crumpled 
  bands 
  of 
  opaque 
  

   light-colored 
  flint 
  and 
  clear 
  amber-colored 
  or 
  black 
  flint, 
  the 
  opaque 
  

   bands 
  are 
  composed 
  mainly 
  of 
  amorphous 
  material 
  like 
  that 
  of 
  the 
  

   softer 
  shale, 
  but 
  in 
  a 
  much 
  more 
  compact 
  state, 
  and 
  the 
  translucent 
  

   bands 
  are 
  mainly 
  crystalline 
  aggregates. 
  The 
  opaque 
  bands 
  include 
  

   crystalline 
  particles 
  and, 
  locally, 
  patches 
  of 
  crystal 
  grains 
  like 
  those 
  

   of 
  the 
  clear 
  flint, 
  and 
  they 
  are 
  included 
  longitudinally 
  by 
  intermittent 
  

   bands 
  of 
  the 
  clear 
  flint. 
  Furthermore, 
  they 
  are 
  in 
  many 
  specimens 
  

   of 
  a 
  patchy 
  appearance, 
  parts 
  being 
  less 
  amorphous 
  than 
  others. 
  

   The 
  bands 
  of 
  the 
  clear 
  flint 
  are 
  composed 
  chiefly 
  of 
  small 
  grains 
  of 
  

   crystalline 
  quartz, 
  and 
  these 
  are 
  surrounded 
  by 
  a 
  finer 
  grained 
  aggre- 
  

   gate 
  of 
  crystalline 
  and 
  amorphous 
  particles. 
  The 
  quartz 
  grains 
  have 
  

   neither 
  the 
  rounded 
  outlines 
  of 
  water 
  worn 
  grains 
  nor 
  angular 
  crystal- 
  

   line 
  outlines, 
  but 
  are 
  branching, 
  and 
  appear 
  more 
  like 
  growths. 
  Angu- 
  

   lar 
  patches 
  of 
  the 
  amorphous 
  silica, 
  many 
  of 
  them 
  showing 
  signs 
  of 
  

  

  