﻿212 
  PROCEEDINGS 
  OP 
  THE 
  CALIFORNIA 
  

  

  front 
  of 
  it 
  sunk 
  at 
  least 
  900 
  or 
  1,000 
  feet. 
  Tlic 
  olifl' 
  is 
  torniiiiatod 
  towards 
  the 
  

   south 
  apparently 
  by 
  a 
  dislocation 
  analogous 
  to 
  that 
  which 
  pushed 
  forward 
  the 
  

   end 
  of 
  the 
  main 
  Tuobla 
  Range, 
  throwing 
  the 
  whole 
  mass 
  of 
  the 
  mountain 
  to 
  

   the 
  cast. 
  At 
  this 
  point 
  the 
  height 
  of 
  the 
  stratified 
  beds 
  was 
  about 
  400 
  feet. 
  

   By 
  this 
  dislocation 
  a 
  pass 
  was 
  formed, 
  by 
  which 
  I 
  was 
  able 
  to 
  reach 
  the 
  upper 
  

   portion 
  of 
  the 
  beds 
  ; 
  they 
  were 
  found 
  covered 
  by 
  a 
  layer 
  of 
  trachyte, 
  and 
  over 
  

   this 
  again 
  were 
  strata 
  of 
  basalt. 
  'I'he 
  probable 
  age 
  of 
  these 
  erupted 
  rocks 
  is 
  

   the 
  early 
  Miocene. 
  'J'he 
  eastern 
  range 
  is 
  probably 
  Triassic, 
  as 
  are 
  the 
  other 
  

   analagous 
  ranges 
  in 
  this 
  ])art 
  of 
  the 
  country. 
  It 
  undoubtedly, 
  at 
  an 
  earlier 
  

   period, 
  extended 
  to 
  join 
  the 
  Vicksburg 
  .Mountains 
  to 
  the 
  south, 
  and, 
  as 
  belbre 
  

   stated, 
  formed 
  part 
  of 
  the 
  eastern 
  shore 
  of 
  a 
  vast 
  basin, 
  in 
  which 
  the 
  beds 
  of 
  

   melted 
  rocks 
  were 
  poured 
  out 
  in 
  eruption 
  after 
  eruption, 
  until 
  they 
  had 
  attained 
  

   a 
  thickness 
  of 
  at 
  least 
  1,.')00 
  feet, 
  and 
  possibly 
  even 
  a 
  greater 
  thickness 
  still, 
  

   as 
  in 
  no 
  place 
  are 
  the 
  lowest 
  of 
  these 
  erupted 
  beds 
  exposed 
  ; 
  iu 
  fact, 
  the 
  min- 
  

   eralogical 
  character 
  of 
  the 
  lower 
  beds 
  would 
  indicate, 
  according 
  to 
  the 
  generally 
  

   received 
  views 
  of 
  geologists, 
  that 
  these 
  l.)eds 
  are 
  but 
  the 
  upper 
  strata 
  of 
  a 
  far 
  

   more 
  extensive 
  eruption. 
  Probably 
  during 
  the 
  latter 
  part 
  of 
  the 
  Miocene 
  era, 
  

   a 
  suspension 
  of 
  volcanic 
  activity 
  occurred, 
  the 
  surface 
  became 
  cooled, 
  and 
  the 
  

   depressed 
  portions 
  of 
  these 
  beds 
  formed 
  the 
  basins 
  of 
  lakes, 
  in 
  which 
  the 
  detritus 
  

   from 
  the 
  surrounding 
  mountains 
  accumulated 
  until 
  it 
  had 
  formed 
  deposits 
  of 
  

   many 
  hundred 
  feet 
  in 
  thickness. 
  After 
  this 
  the 
  strata 
  became 
  displaced, 
  as 
  we 
  

   now 
  find 
  them. 
  This 
  displacement 
  was 
  caused, 
  I 
  think, 
  by 
  a 
  sinking 
  to 
  the 
  

   west, 
  by 
  which 
  the 
  eastern 
  edge 
  of 
  the 
  beds 
  were 
  tilted 
  up, 
  and 
  a 
  fracture 
  was 
  

   produced 
  along 
  the 
  line 
  where 
  they 
  were 
  in 
  contact 
  with 
  the 
  schists 
  and 
  por- 
  

   phyries 
  of 
  what 
  now 
  forms 
  the 
  eastern 
  ridge. 
  The 
  valley 
  between 
  the 
  two 
  

   ridges 
  was 
  thus 
  made, 
  and 
  a 
  subsequent 
  volcanic 
  outburst, 
  the 
  axis 
  of 
  which 
  

   was 
  from 
  east 
  to 
  west, 
  threw 
  up 
  a 
  ridge 
  dividing 
  the 
  valley 
  into 
  two 
  parts, 
  and 
  

   elevating 
  that 
  part 
  of 
  the 
  volcanic 
  range, 
  under 
  which 
  it 
  occurred, 
  some 
  800 
  or 
  

   1,000 
  feet, 
  without 
  apparently 
  disturbing 
  the 
  older 
  range 
  to 
  the 
  cast. 
  Subse- 
  

   quently, 
  this 
  valley 
  has 
  suffered 
  cojisiderable 
  erosion, 
  and 
  at 
  one 
  time 
  must 
  have 
  

   been 
  filled 
  by 
  a 
  vast 
  glacier, 
  which 
  flowed 
  out 
  over 
  the 
  southern 
  part 
  of 
  the 
  

   eastern 
  range, 
  depositing 
  a 
  moraine 
  2.50 
  feet 
  thick, 
  which 
  extends 
  a 
  mile 
  and 
  

   a 
  half 
  into 
  the 
  plain 
  beyond 
  the 
  base 
  of 
  the 
  mountain. 
  

  

  Such 
  is 
  a 
  general 
  outline 
  of 
  the 
  more 
  nuvrked 
  geological 
  features 
  of 
  the 
  

   Puebla 
  Range, 
  and 
  I 
  now 
  shall 
  proceed 
  to 
  olTer 
  a 
  few 
  remarks 
  on 
  the 
  minera- 
  

   logical 
  character 
  and 
  chemical 
  composition 
  of 
  the 
  erupted 
  rocks 
  which 
  consti- 
  

   tute 
  its 
  western 
  ridge. 
  

  

  As 
  before 
  stated, 
  this 
  ridge 
  is 
  composed 
  of 
  diflerent 
  beds 
  of 
  erupted 
  rocks, 
  

   •which 
  are 
  perfectly 
  conformable, 
  and 
  have 
  evidently 
  been 
  ejected 
  at 
  dif- 
  

   ferent 
  periods 
  of 
  what 
  nuist 
  be 
  considered 
  the 
  same 
  volcanic 
  era. 
  Their 
  

   number 
  it 
  is 
  diOQcult 
  to 
  state, 
  as 
  the 
  softer 
  of 
  them, 
  by 
  their 
  more 
  rapid 
  disin- 
  

   tegration, 
  have 
  covered 
  the 
  side 
  of 
  the 
  mountain 
  for 
  considerable 
  space 
  with 
  

   fine 
  ash-like 
  powder, 
  which, 
  as 
  it 
  never 
  rains 
  in 
  these 
  regions, 
  has 
  no 
  chance 
  of 
  

   being 
  washed 
  away, 
  and 
  can 
  only 
  be 
  removed 
  in 
  the 
  form 
  of 
  dust 
  by 
  the 
  wind. 
  

   It 
  is 
  only 
  the 
  harder 
  and 
  more 
  resisting 
  layers 
  that 
  are 
  exposed, 
  as 
  from 
  these 
  

  

  