﻿42 
  SANTA 
  MARIA 
  OIL 
  DISTRICT, 
  CALIFORNIA. 
  

  

  those 
  observed 
  under 
  the 
  microscope 
  being 
  only 
  fragments, 
  and 
  this 
  

   makes 
  it 
  probable 
  thai 
  others 
  are 
  still 
  more 
  fragmentary 
  and 
  in 
  a 
  

   state 
  of 
  complete 
  demolition. 
  The 
  likelihood, 
  therefore, 
  is 
  that 
  a 
  

   greater 
  proportion 
  of 
  the 
  pure 
  shale 
  than 
  5 
  to 
  10 
  per 
  cent, 
  as 
  roughly 
  

   estimated 
  by 
  Mr. 
  Keeley 
  on 
  the 
  basis 
  of 
  visible 
  forms, 
  is 
  composed 
  

   of 
  silica 
  derived 
  from 
  diatoms. 
  Radiolaria, 
  which 
  are 
  scattered 
  

   through 
  the 
  shale 
  sparingly, 
  have 
  contributed 
  somewhat 
  to 
  the 
  organic 
  

   silica. 
  Whatever 
  conclusion 
  one 
  should 
  come 
  to 
  would 
  apply 
  to 
  almost 
  

   all 
  of 
  the 
  soft 
  unaltered 
  shale 
  of 
  the 
  siliceous 
  type 
  in 
  the 
  Monterey 
  of 
  

   the 
  Santa 
  Maria 
  district, 
  as 
  this 
  type 
  is 
  fairly 
  constant. 
  Locally 
  it 
  is 
  

   varied 
  by 
  an 
  increased 
  proportion 
  of 
  argillaceous 
  material, 
  causing 
  a 
  

   greater 
  similarity 
  in 
  appearance 
  to 
  ordinary 
  clay 
  shale, 
  or 
  by 
  the 
  

   presence 
  of 
  lime; 
  but 
  diatoms 
  are 
  visible 
  in 
  practically 
  all 
  of 
  it 
  and 
  the 
  

   general 
  conditions 
  of 
  deposition 
  seem 
  to 
  have 
  been 
  the 
  same 
  through- 
  

   out. 
  The 
  conclusion 
  is 
  reached 
  elsewhere 
  (p. 
  47) 
  that 
  the 
  same 
  prob- 
  

   able 
  origin 
  may 
  be 
  assigned 
  to 
  all 
  the 
  siliceous 
  shales 
  of 
  the 
  Monterey, 
  

   whether 
  hard 
  or 
  soft 
  — 
  or, 
  in 
  other 
  words, 
  to 
  by 
  far 
  the 
  greater 
  part 
  of 
  

   the 
  formation. 
  

  

  The 
  list 
  of 
  organic 
  constituents 
  of 
  the 
  shale 
  is 
  by 
  no 
  means 
  exhausted 
  

   by 
  the 
  small 
  organisms 
  of 
  low 
  order 
  so 
  far 
  mentioned. 
  Another 
  

   important 
  source 
  of 
  silica 
  lies 
  in 
  the 
  abundant 
  sponge 
  spicules, 
  which 
  

   are 
  only 
  second 
  in 
  number 
  to 
  the 
  diatoms 
  and 
  which 
  are 
  scattered 
  

   with 
  remarkable 
  persistency 
  throughout 
  the 
  shale. 
  In 
  the 
  slightly 
  

   gritty 
  beds 
  of 
  soft 
  shale, 
  which 
  occur 
  sparingly, 
  these 
  spicules 
  even 
  

   predominate 
  over 
  the 
  diatoms, 
  being 
  possibly 
  the 
  cause 
  of 
  the 
  grit- 
  

   tiness. 
  They 
  seem 
  also 
  to 
  be 
  less 
  easily 
  obliterated 
  than 
  the 
  fragile 
  

   diatom 
  shells 
  and 
  to 
  have 
  been 
  preserved 
  in 
  places 
  where 
  slight 
  alter- 
  

   ation 
  of 
  the 
  rock 
  has 
  destroyed 
  the 
  latter. 
  One 
  of 
  the 
  commonest 
  

   and 
  most 
  characteristic 
  features 
  of 
  both 
  the 
  immetamorphosed 
  sili- 
  

   ceous 
  and 
  the 
  calcareous 
  shales 
  is 
  the 
  presence 
  of 
  scales 
  of 
  fish, 
  show- 
  

   ing 
  that 
  fish 
  remains 
  found 
  their 
  way 
  to 
  the 
  ooze 
  at 
  the 
  ocean 
  bottom 
  

   in 
  greater 
  or 
  less 
  abundance. 
  Locally 
  the 
  bones 
  and 
  nearly 
  complete 
  

   skeletons 
  are 
  also 
  to 
  be 
  found. 
  Delicate 
  mollusk 
  shells, 
  usually 
  of 
  

   small 
  size, 
  are 
  gathered 
  thickly 
  in 
  some 
  places 
  in 
  the 
  Monterey 
  shale, 
  

   and 
  at 
  such 
  points 
  may 
  be 
  considered 
  as 
  constituting 
  an 
  appreciable 
  

   proportion 
  of 
  the 
  total 
  volume 
  of 
  the 
  deposit. 
  As 
  a 
  rule 
  they 
  are 
  

   crushed 
  and 
  poorly 
  preserved, 
  a 
  fact 
  that 
  lends 
  weight 
  to 
  the 
  theory 
  

   that 
  a 
  large 
  part 
  of 
  the 
  diatom 
  frustules 
  also 
  have 
  been 
  destroyed. 
  

   But 
  mollusks 
  are 
  rare 
  in 
  the 
  formation 
  as 
  a 
  whole. 
  Crab 
  shells 
  and 
  

   claws 
  are 
  occasionally 
  found, 
  usually 
  not 
  whole 
  but 
  in 
  small 
  pieces, 
  

   as 
  if 
  they 
  had 
  been 
  subjected 
  to 
  conditions 
  favorable 
  to 
  their 
  destruc- 
  

   tion 
  before 
  coming 
  to 
  rest. 
  Seaweed 
  impressions 
  are 
  not 
  rare. 
  In 
  

   addition 
  to 
  organic 
  remains 
  of 
  these 
  kinds, 
  the 
  shales, 
  especially 
  the 
  

  

  