﻿GEOLOGY. 
  69 
  

  

  period. 
  Acidic 
  volcanic 
  ash 
  of 
  a 
  rhyolitic 
  type 
  was 
  ejected, 
  and 
  it 
  

   settled 
  in 
  the 
  ocean 
  to 
  form 
  regular 
  beds 
  of 
  considerable 
  thickness 
  

   and 
  extent 
  interstratified 
  with 
  the 
  other 
  sediments. 
  The 
  occur- 
  

   rence 
  of 
  ash 
  interbedded 
  with 
  diatomaceous 
  earth 
  that 
  probably 
  

   belongs 
  fairly 
  high 
  in 
  the 
  Monterey 
  formation 
  indicates 
  that 
  these 
  

   eruptions 
  did 
  not 
  cease 
  in 
  the 
  early 
  part 
  of 
  middle 
  Miocene 
  time. 
  

   Neither 
  the 
  centers 
  of 
  eruptions 
  nor 
  any 
  lava 
  equivalents 
  of 
  the 
  ash 
  

   have 
  been 
  found 
  in 
  the 
  field. 
  Similar 
  eruptions 
  were 
  characteristic 
  

   of 
  the 
  lower 
  and 
  middle 
  Miocene 
  for 
  long 
  distances 
  north 
  and 
  south 
  

   of 
  this 
  region. 
  

  

  LATE 
  TERTIARY 
  AND 
  EARLY 
  QUATERNARY 
  PERIOD. 
  

  

  The 
  Monterey 
  period 
  of 
  deposition 
  was 
  brought 
  to 
  a 
  close 
  by 
  

   orogenic 
  movements 
  which 
  folded 
  the 
  shales 
  and 
  lifted 
  them 
  above 
  

   the 
  sea 
  in 
  many 
  places. 
  In 
  some 
  regions 
  the 
  folding 
  was 
  intense, 
  

   the 
  greatest 
  disturbances 
  accompanying 
  the 
  uplift 
  of 
  the 
  mountain 
  

   ranges 
  to 
  an 
  altitude 
  of 
  thousands 
  of 
  feet. 
  The 
  San 
  Rafael 
  Moun- 
  

   tains, 
  which 
  were 
  upheaved 
  at 
  this 
  time, 
  probably 
  extended 
  along 
  

   the 
  lines 
  of 
  former 
  mountains, 
  and 
  some 
  smaller 
  mountainous 
  or 
  

   hilly 
  areas 
  likewise, 
  such 
  as 
  the 
  Casmalia 
  Hills 
  and 
  perhaps 
  portions 
  

   of 
  the 
  Santa 
  Ynez 
  Range, 
  followed 
  former 
  zones 
  of 
  uplift. 
  But 
  for 
  

   the 
  most 
  part 
  the 
  Santa 
  Ynez 
  Range 
  was 
  probably 
  new. 
  It 
  is 
  

   doubtful 
  whether 
  it 
  was 
  ever 
  completely 
  covered 
  by 
  Monterey 
  sedi- 
  

   ments, 
  and 
  its 
  structure 
  may 
  have 
  been 
  determined 
  by 
  minor 
  folding 
  

   previous 
  to 
  the 
  beginning 
  of 
  the 
  Monterey, 
  but 
  it 
  is 
  probable 
  that 
  

   this 
  range 
  did 
  not 
  have 
  any 
  approach 
  to 
  its 
  present 
  proportions 
  until 
  

   after 
  middle 
  Miocene 
  time. 
  In 
  other 
  regions 
  low, 
  broad 
  folds 
  were 
  

   formed 
  during 
  the 
  post-Monterey 
  disturbance 
  and 
  the 
  strata 
  were 
  

   not 
  upheaved 
  to 
  a 
  great 
  altitude* 
  such 
  was 
  the 
  case 
  in 
  parts 
  of 
  the 
  

   basin 
  region 
  between 
  the 
  San 
  Rafael 
  and 
  Santa 
  Ynez 
  mountains. 
  

  

  After 
  the 
  formation 
  of 
  the 
  middle 
  Miocene 
  shales 
  they 
  were 
  

   intruded 
  at 
  several 
  different 
  points 
  by 
  basic 
  igneous 
  masses, 
  mostly 
  

   of 
  the 
  nature 
  of 
  diabase. 
  The 
  disturbance 
  which 
  put 
  an 
  end 
  to 
  the 
  

   period 
  was 
  profound 
  and 
  this 
  igneous 
  activity 
  was 
  probably 
  an 
  

   accompaniment 
  of 
  it. 
  The 
  rocks 
  were 
  locally 
  hardened 
  by 
  contact 
  N 
  

   action 
  in 
  consequence 
  of 
  the 
  intrusions. 
  

  

  After 
  an 
  erosion 
  interval, 
  probably 
  of 
  comparatively 
  short 
  dura- 
  

   tion, 
  the 
  land 
  again 
  sank, 
  though 
  not 
  so 
  extensively 
  nor 
  to 
  such 
  

   depth 
  as 
  in 
  the 
  previous 
  subsidence, 
  and 
  a 
  large 
  part 
  of 
  the 
  Santa 
  

   Maria 
  district, 
  especially 
  the 
  lower 
  regions, 
  became 
  submerged. 
  

   The 
  deposition 
  of 
  the 
  Fernando 
  followed, 
  beginning 
  before 
  the 
  close 
  

   of 
  the 
  Miocene. 
  Owing 
  to 
  differences 
  in 
  altitude 
  and 
  possibly 
  also 
  

   to 
  local 
  difference 
  in 
  the 
  amount 
  of 
  subsidence, 
  the 
  deposition 
  began 
  

   in 
  some 
  places 
  before 
  it 
  did 
  in 
  others. 
  Over 
  the 
  areas 
  in 
  which 
  the 
  

   Monterey 
  has 
  been 
  only 
  slightly 
  folded, 
  the 
  Fernando 
  beds 
  assumed 
  

   conformable 
  positions 
  with 
  it. 
  In 
  regions 
  where 
  the 
  Monterey 
  beds 
  

  

  