﻿34 
  SANTA 
  MA 
  IMA 
  oil, 
  DISTRICT, 
  CALIFORNIA. 
  

  

  unaltered 
  condition 
  il 
  resembles 
  chalk, 
  but 
  is 
  of 
  siliceous 
  instead 
  of 
  

   calcareous 
  composition. 
  

  

  The 
  Monterey 
  in 
  the 
  part 
  of 
  California 
  treated 
  here 
  may 
  be 
  divided 
  

   on 
  lithologic 
  grounds 
  into 
  two 
  parts, 
  although 
  there 
  seems 
  to 
  be 
  per- 
  

   fect 
  conformity 
  throughout 
  the 
  series. 
  There 
  is 
  no 
  definite 
  dividing 
  

   line 
  4 
  to 
  be 
  drawn, 
  but 
  taken 
  as 
  a 
  whole 
  the 
  low 
  r 
  er 
  half, 
  composed 
  

   chiefly 
  of 
  hard, 
  metamorphosed, 
  in 
  places 
  flinty 
  shales, 
  is 
  distinct 
  

   from 
  the 
  upper 
  half, 
  in 
  which 
  soft 
  shale, 
  giving 
  evidence 
  to 
  the 
  naked 
  

   eye 
  of 
  its 
  organic 
  origin, 
  is 
  predominant. 
  

  

  LOWER 
  DIVISION. 
  

  

  The 
  fossiliferous 
  limestone 
  at 
  the 
  top 
  of 
  the 
  Vaqueros 
  is 
  overlain 
  

   conformably 
  by 
  hard 
  calcareous 
  and 
  flinty 
  unfossiliferous 
  shale 
  char- 
  

   acteristic 
  of 
  the 
  base 
  of 
  the 
  Monterey. 
  In 
  places 
  the 
  limestone 
  at 
  

   the 
  top 
  of 
  the 
  Vaqueros 
  is 
  not 
  well 
  developed, 
  but 
  is 
  replaced 
  by 
  a 
  

   series 
  of 
  thin-bedded, 
  in 
  the 
  main 
  fairly 
  hard, 
  siliceous, 
  calcareous, 
  

   and 
  somewhat 
  argillaceous 
  shales 
  of 
  coarse 
  and 
  fine 
  texture, 
  in 
  which 
  

   no 
  well-defined 
  line 
  of 
  demarcation 
  between 
  the 
  two 
  formations 
  is 
  to 
  

   be 
  drawn. 
  The 
  Vaqueros 
  and 
  Monterey 
  terranes 
  taken 
  as 
  wholes 
  

   are 
  distinct 
  units, 
  representing 
  periods 
  of 
  deposition 
  of 
  entirely 
  differ- 
  

   ent 
  character. 
  As 
  indicated 
  by 
  the 
  rocks, 
  deposition 
  w 
  T 
  as 
  continuous 
  

   between 
  the 
  Vaqueros 
  and 
  Monterey 
  and 
  the 
  change 
  in 
  character 
  

   came 
  suddenly, 
  although 
  less 
  so 
  in 
  some 
  places 
  than 
  in 
  others. 
  The 
  

   general 
  nature 
  of 
  the 
  Vaqueros 
  series 
  is 
  detrital; 
  that 
  of 
  the 
  Mon- 
  

   terey 
  is 
  organic. 
  The 
  former 
  contains 
  many 
  well-preserved 
  mollus- 
  

   can 
  forms, 
  the 
  latter 
  few.' 
  Close 
  to 
  the 
  line 
  between 
  the 
  two, 
  beds 
  

   predominatingly 
  of 
  a 
  gravelly 
  or 
  sandy 
  nature 
  or 
  those 
  bearing 
  fossil 
  

   mollusks 
  are 
  considered 
  part 
  of 
  the 
  Vaqueros; 
  those 
  of 
  a 
  fine 
  texture 
  

   and 
  of 
  flinty 
  or 
  opaline 
  or 
  chalcedonic 
  nature, 
  part 
  of 
  the 
  Monterey. 
  

  

  Above 
  the 
  transitional 
  limestone 
  horizon 
  between 
  the 
  Vaqueros 
  

   and 
  Monterey 
  the 
  lower 
  half 
  of 
  the 
  latter 
  formation 
  consists 
  of 
  a 
  

   thick 
  series 
  of 
  thin-bedded, 
  hard, 
  brittle, 
  siliceous 
  and 
  calcareous 
  

   shales, 
  with 
  local 
  gradations 
  on 
  the 
  one 
  hand 
  into 
  beds 
  of 
  the 
  hardest 
  

   flint 
  and 
  on 
  the 
  other 
  into 
  soft 
  diatomaceous 
  earth. 
  Near 
  the 
  base 
  

   there 
  is 
  usually 
  a 
  horizon 
  of 
  black, 
  brownish, 
  or 
  wax-colored 
  flint 
  

   in 
  heavy 
  beds 
  one 
  to 
  several 
  feet 
  thick, 
  and 
  similar 
  massive 
  beds 
  of 
  

   peculiar 
  sand-colored 
  limestone 
  with 
  characteristic 
  lamellar 
  weath- 
  

   ering. 
  The 
  greater 
  part 
  of 
  the 
  series 
  is 
  made 
  up 
  of 
  brittle 
  siliceous 
  

   shale, 
  usually 
  much 
  fractured 
  and 
  rather 
  commonly 
  crumpled, 
  in 
  

   beds 
  averaging 
  about 
  one-half 
  to 
  1 
  inch 
  in 
  thickness, 
  in 
  places 
  alter- 
  

   nating 
  with 
  thin 
  shaly 
  calcareous 
  beds 
  or 
  massive 
  strata 
  of 
  lime- 
  

   stone. 
  Pis. 
  Ill, 
  B, 
  and 
  VI, 
  B 
  (p. 
  46), 
  show 
  outcrops 
  of 
  typical 
  flinty 
  

   shale 
  of 
  the 
  lower 
  division. 
  Beds 
  of 
  flinty 
  shale 
  or 
  of 
  pure 
  flint 
  are 
  

   included 
  here 
  and 
  there. 
  The 
  flint 
  is 
  of 
  different 
  colors 
  — 
  amber, 
  black, 
  

   milky, 
  red, 
  brown, 
  etc. 
  — 
  and 
  of 
  different 
  degrees 
  of 
  translucency. 
  

   Much 
  of 
  it 
  has 
  been 
  fractured 
  and 
  recemented 
  with 
  chalcedonic 
  veins. 
  

  

  