﻿GEOLOGY. 
  

  

  67 
  

  

  uplift 
  did 
  not 
  occur 
  at 
  the 
  close 
  of 
  Eocene 
  time, 
  but 
  it 
  is 
  probable 
  

   that 
  orogenic 
  movements 
  did 
  bring 
  to 
  a 
  close 
  the 
  period 
  during 
  

   which 
  the 
  Eocene 
  sediments 
  were 
  laid 
  down 
  by 
  raising 
  the 
  strata 
  

   slightly 
  above 
  the 
  sea 
  and 
  preventing 
  for 
  a 
  time 
  further 
  deposition. 
  

   How 
  long 
  this 
  time 
  was 
  is 
  not 
  known, 
  but 
  it 
  corresponds 
  approxi- 
  

   mately 
  with 
  the 
  Oligocene. 
  

  

  LOWER 
  MIOCENE 
  PERIOD. 
  

  

  The 
  movements 
  immediately 
  following 
  the 
  deposition 
  of 
  the 
  

   Eocene 
  caused 
  no 
  appreciable 
  disturbance 
  in 
  the 
  Eocene 
  strata, 
  and 
  

   when 
  sedimentation 
  recommenced 
  over 
  the 
  same 
  area 
  in 
  lower 
  

   Miocene 
  time 
  neither 
  the 
  old 
  nor 
  the 
  new 
  strata 
  preserved 
  any 
  posi- 
  

   tive 
  evidence 
  in 
  their 
  relative 
  position 
  that 
  a 
  time 
  break 
  had 
  occurred. 
  

   The 
  great 
  masses 
  of 
  coarse 
  conglomerate 
  forming 
  the 
  base 
  of 
  the 
  

   lower 
  Miocene 
  portion 
  of 
  the 
  group 
  record 
  a 
  change 
  to 
  conditions 
  

   of 
  very 
  shallow 
  water, 
  and 
  the 
  abrupt 
  change 
  of 
  faunas 
  indicates 
  

   that 
  a 
  long 
  time 
  interval 
  separated 
  their 
  deposition 
  from 
  that 
  of 
  the 
  

   'subjacent 
  Eocene. 
  It 
  is 
  most 
  probable, 
  however, 
  that 
  the 
  post- 
  

   Eocene 
  movements, 
  which 
  were 
  gentle, 
  were 
  also 
  somewhat 
  local, 
  

   and 
  that 
  in 
  portions 
  of 
  the 
  Santa 
  Ynez 
  Mountains 
  to 
  the 
  east 
  of 
  the 
  

   region 
  under 
  discussion 
  sedimentation 
  was 
  more 
  nearly 
  continuous. 
  

   At 
  about 
  the 
  close 
  of 
  the 
  Oligocene 
  period 
  the 
  Eocene 
  basin 
  was 
  

   again 
  depressed; 
  deposition 
  of 
  sediments, 
  almost 
  entirely 
  of 
  detntal 
  

   origin 
  and 
  very 
  similar 
  to 
  those 
  previously 
  laid 
  down, 
  ensued 
  in 
  a 
  

   widening 
  area 
  covered 
  by 
  the 
  sea; 
  and 
  subsidence 
  of 
  the 
  land 
  gradu- 
  

   ally 
  continued. 
  The 
  Vaqueros 
  formation, 
  which 
  resulted 
  from 
  this 
  

   period 
  of 
  depression, 
  represents 
  the 
  greater 
  part 
  of 
  lower 
  Miocene 
  

   time. 
  

  

  MIDDLE 
  MIOCENE 
  PERIOD. 
  

  

  The 
  middle 
  Miocene 
  (Monterey) 
  shale 
  formation 
  is 
  one 
  of 
  striking 
  

   individuality, 
  and 
  conditions 
  of 
  unusual 
  character 
  prevailed 
  during 
  

   its 
  period 
  of 
  deposition. 
  At 
  the 
  beginning 
  of 
  middle 
  Miocene 
  time 
  

   the 
  land 
  sank 
  over 
  a 
  large 
  part 
  of 
  the 
  region 
  of 
  California 
  now 
  occu- 
  

   pied 
  by 
  the 
  Coast 
  Ranges 
  and 
  fairly 
  deep 
  water 
  conditions 
  became 
  

   prevalent 
  The 
  wearing 
  away 
  of 
  extended 
  land 
  areas 
  ceased 
  as 
  they 
  

   became 
  submerged, 
  and 
  the 
  material 
  for 
  the 
  formation 
  of 
  coarse 
  

   detrital 
  deposits 
  was 
  no 
  longer 
  plentiful. 
  Two 
  varieties 
  of 
  deposits 
  

   which 
  were 
  largely 
  of 
  organic 
  origin, 
  were 
  the 
  chief 
  ones 
  to 
  be 
  formed 
  

   during 
  the 
  long 
  period 
  that 
  followed. 
  These 
  were 
  the 
  laminated 
  

   limestones 
  and 
  the 
  much 
  more 
  abundant 
  siliceous 
  shales. 
  Silt 
  oi 
  

   extremely 
  fine 
  grain, 
  both 
  of 
  siliceous 
  and 
  argillaceous 
  nature, 
  was 
  

   swept 
  into 
  the 
  sea 
  waters, 
  probably 
  from 
  considerable 
  distances, 
  and 
  

   settled 
  down 
  to 
  form 
  a 
  considerable 
  proportion 
  of 
  the 
  deposits; 
  but 
  

   sand 
  and 
  other 
  coarse 
  detritus 
  found 
  their 
  way 
  only 
  at 
  rare 
  intervals 
  

  

  