﻿216 
  

  

  PROCEEDINGS 
  OP 
  THE 
  CALIFORNIA 
  

  

  conglomerate 
  M-as 
  seen. 
  Uniloiibted 
  evidence 
  was 
  also 
  found 
  that 
  the 
  upper 
  

   surface 
  of 
  the 
  conglomerate 
  (c) 
  was 
  an 
  old 
  eroded 
  land-surface, 
  upon 
  which 
  the 
  

   lava 
  was 
  outpoured. 
  

  

  There 
  can 
  be 
  no 
  doubt, 
  

   therefore, 
  that 
  (h) 
  marks 
  the 
  

   place 
  of 
  an 
  old 
  forest 
  ground, 
  

   upon 
  which 
  grew 
  the 
  trees, 
  

   whose 
  stumps 
  still 
  remain 
  in 
  a 
  

   siliciSed 
  condition, 
  before 
  the 
  

   lava 
  was 
  outpoured 
  ; 
  and 
  that 
  

   the 
  leaves 
  of 
  the 
  stratum 
  (c) 
  

   are 
  those 
  of 
  these 
  or 
  contem- 
  

   poraneous 
  trees. 
  The 
  order 
  of 
  

   events 
  seems 
  to 
  have 
  been 
  : 
  1. 
  

   A 
  forest 
  of 
  oak 
  and 
  conifers. 
  

   2. 
  The 
  destruction 
  of 
  the 
  trees 
  

   by 
  water, 
  the 
  shedding 
  and 
  

   burying 
  of 
  the 
  leaves, 
  and 
  the 
  

   rotting 
  of 
  the 
  trunks 
  to 
  stumps. 
  3. 
  The 
  covering 
  of 
  the 
  place 
  several 
  hundred 
  

   feet 
  with 
  coarse 
  deposit 
  [d). 
  4. 
  The 
  erosion 
  of 
  this 
  second 
  land-surface 
  (e) 
  into 
  

   bill 
  and 
  dale. 
  5. 
  The 
  outpouring 
  of 
  the 
  lava, 
  layer 
  upon 
  layer, 
  for 
  a 
  long 
  

   period 
  of 
  time. 
  6. 
  Finally, 
  the 
  erosion 
  of 
  the 
  streams 
  — 
  whether 
  as 
  ice 
  or 
  water, 
  

   or 
  both— 
  through 
  the 
  3.000 
  feet 
  of 
  lava 
  into 
  the 
  underlying 
  soil. 
  It 
  is 
  this 
  last 
  

   fact, 
  viz 
  : 
  the 
  cutting 
  through 
  the 
  lava 
  into 
  the 
  softer 
  underlying 
  conglomerate, 
  

   which 
  determines 
  the 
  existence 
  of 
  the 
  cascades 
  of 
  the 
  main 
  river, 
  and 
  also 
  the 
  

   perpendicular 
  falls 
  at 
  the 
  heads 
  of 
  the 
  tributary 
  stream 
  gorges. 
  

  

  III. 
  — 
  Age 
  of 
  the 
  Cascade 
  Range. 
  

  

  There 
  has 
  been 
  much 
  doubt 
  as 
  to 
  the 
  age 
  of 
  the 
  Cascade 
  Mountains. 
  The 
  

   author 
  thinks 
  the 
  leaf 
  bed 
  (c) 
  furnishes 
  the 
  means 
  of 
  determining 
  this 
  question 
  

   with 
  considerable 
  certainty. 
  A 
  number 
  of 
  specimens 
  of 
  leaf 
  impressions 
  and 
  

   silicified 
  wood, 
  gathered 
  by 
  him, 
  were 
  sent 
  to 
  Prof. 
  Lesquereux. 
  According 
  to 
  

   this 
  high 
  authority, 
  they 
  are 
  leaves 
  and 
  wood 
  of 
  species 
  of 
  oak 
  and 
  conifers, 
  

   which 
  indicate 
  certainly 
  Tertiary, 
  most 
  probably 
  Miocene, 
  The 
  lava-flood, 
  there- 
  

   fore, 
  occurred 
  during 
  or 
  after 
  the 
  Miocene. 
  But 
  since 
  the 
  upper 
  surface 
  of 
  the 
  

   conglomerate 
  is 
  an 
  old 
  eroded 
  land-surface, 
  requiring 
  much 
  time 
  for 
  its 
  erosion, 
  

   it 
  is 
  most 
  probable 
  that 
  the 
  lava 
  flood 
  occurred, 
  or 
  began 
  to 
  occur, 
  at 
  the 
  end 
  of 
  

   the 
  Miocene. 
  This 
  would 
  make 
  it 
  coincident 
  wilh 
  the 
  foi-maiion 
  of 
  the 
  Coast 
  

   range. 
  It 
  began 
  to 
  occur 
  then 
  ; 
  but 
  it 
  continued 
  by 
  the 
  outpouring 
  of 
  suc- 
  

   cesBive 
  layers, 
  building 
  higher 
  and 
  higher, 
  probably, 
  until 
  the 
  end 
  of 
  the 
  

   Tertiary. 
  

  

  The 
  height 
  of 
  the 
  passes 
  of 
  the 
  Cascade 
  range 
  is 
  not 
  more 
  than 
  4,000 
  or 
  .5,000 
  

   feet 
  ; 
  but 
  the 
  lava 
  is 
  3,000 
  to 
  4,000 
  feet 
  thick. 
  Evidently, 
  then, 
  the 
  great 
  bulk 
  

   of 
  this 
  range 
  is 
  of 
  late 
  Tertiary 
  origin. 
  But 
  the 
  range 
  probably 
  existed 
  before 
  

   this 
  as 
  a 
  low 
  range 
  of 
  granite 
  and 
  slate, 
  like 
  the 
  Sierras, 
  and 
  of 
  the 
  same 
  age. 
  

  

  