﻿214 
  PROCEEDINGS 
  OP 
  THE 
  CALIFORNIA 
  

  

  vesicular 
  tracliytf", 
  the 
  amount 
  of 
  silica 
  is 
  5G.2 
  per 
  cent. 
  ; 
  in 
  the 
  labrador 
  por- 
  

   phyry, 
  49 
  per 
  cent. 
  ; 
  in 
  the 
  diabase, 
  No. 
  6, 
  51 
  per 
  cent. 
  ; 
  in 
  the 
  green 
  trachyte, 
  

   72 
  per 
  cent. 
  ; 
  in 
  the 
  black 
  porphyritic 
  obsidian, 
  63 
  per 
  cent. 
  ; 
  and 
  in 
  the 
  

   anamesite, 
  No. 
  4, 
  44 
  per 
  cent. 
  

  

  It 
  is 
  evident 
  from 
  the 
  above 
  facts 
  that 
  the 
  relative 
  position 
  of 
  these 
  different 
  

   beds 
  is 
  not 
  in 
  accordance 
  with 
  the 
  views 
  advanced 
  by 
  Richthofen.in 
  his 
  memoir, 
  

   which 
  was 
  published 
  by 
  the 
  Academy 
  in 
  18G8. 
  In 
  this 
  memoir 
  it 
  is 
  stated 
  

   that 
  in 
  massive 
  eruptions, 
  of 
  which 
  the 
  Puebla 
  volcanic 
  range 
  presents 
  so 
  

   striking 
  an 
  example, 
  the 
  basaltic 
  rocks 
  are 
  always 
  the 
  last 
  to 
  be 
  thrown 
  up, 
  so 
  

   that 
  they 
  invariably 
  form 
  the 
  upper 
  beds 
  in 
  all 
  such 
  eruptions. 
  Here, 
  however, 
  

   we 
  find 
  true 
  basaltic 
  beds, 
  occupying 
  positions 
  below 
  other 
  erupted 
  rocks, 
  

   occurring 
  between 
  beds 
  of 
  porphyry 
  and 
  diabase, 
  aud 
  even 
  directly 
  under 
  beds 
  

   of 
  a 
  trachytic 
  character. 
  There 
  can 
  be 
  no 
  doubt 
  but 
  that 
  Richthofen's 
  system 
  

   of 
  volcanic 
  rocks 
  is 
  but 
  an 
  expression 
  of 
  facts, 
  as 
  presented 
  by 
  a 
  large 
  part 
  

   of 
  the 
  massive 
  eruptions 
  whose 
  geological 
  history 
  has 
  been 
  carefully 
  investigated. 
  

   That 
  the 
  system, 
  however, 
  does 
  not 
  apply 
  to 
  the 
  Puebla 
  range 
  of 
  mountains, 
  is, 
  

   I 
  think, 
  beyond 
  a 
  doubt 
  ; 
  and 
  I 
  expect 
  the 
  geological 
  formation 
  of 
  this 
  range 
  

   will 
  be 
  found 
  repeated 
  in 
  the 
  vast 
  outflows 
  of 
  volcanic 
  rocks 
  that 
  cover 
  so 
  large 
  

   a 
  portion 
  of 
  eastern 
  Oregon, 
  extending 
  north 
  beyond 
  the 
  Columbia 
  River.* 
  

  

  The 
  mineralogical 
  character 
  and 
  chemical 
  composition 
  of 
  these 
  Puebla 
  beds 
  

   is 
  so 
  interesting, 
  that 
  I 
  hope 
  at 
  some 
  future 
  time 
  to 
  bring 
  before 
  the 
  Academy 
  

   a 
  more 
  complete 
  account 
  of 
  my 
  investigations 
  ou 
  this 
  subject. 
  

  

  Professor 
  Joseph 
  Le 
  Conte 
  read 
  the 
  following 
  : 
  

  

  On 
  the 
  Great 
  Lava- 
  Flood 
  of 
  the 
  Northwest, 
  and 
  on 
  the 
  

   Structure 
  and 
  Age 
  of 
  the 
  Cascade 
  Mountains. 
  

  

  . 
  BY 
  JOSEPH 
  LE 
  CONTR, 
  

   Professor 
  of 
  Geology 
  in 
  the 
  University 
  of 
  California. 
  

  

  ABSTRACT. 
  

   I. 
  — 
  Lava-Fi,ood 
  of 
  the 
  Northwest. 
  

  

  The 
  author 
  stated, 
  that 
  in 
  the 
  summers 
  of 
  1871 
  and 
  1873 
  he 
  made 
  a 
  geo- 
  

   logical 
  tour 
  through 
  portions 
  of 
  Oregon 
  and 
  Washington, 
  the 
  object 
  of 
  which 
  

   was 
  to 
  study 
  the 
  lava-flood 
  of 
  this 
  region, 
  aud 
  especially 
  the 
  structure 
  of 
  the 
  

   Cascade 
  range. 
  He 
  attributes 
  much 
  of 
  his 
  success 
  to 
  the 
  kind 
  assistance 
  of 
  

   Rev. 
  Mr. 
  Condon, 
  the 
  geologist 
  of 
  Oregon. 
  

  

  * 
  From 
  the 
  highest 
  point 
  of 
  the 
  ridge, 
  as 
  far 
  as 
  could 
  be 
  seen, 
  the 
  country 
  to 
  the 
  

   north 
  and 
  west 
  presented 
  the 
  appearance 
  of 
  a 
  purely 
  volcanic 
  country. 
  Vast 
  faults 
  

   were 
  visible 
  to 
  the 
  west, 
  and 
  when 
  near 
  enough 
  to 
  be 
  made 
  out, 
  presenting 
  sections 
  of 
  

   horizontal 
  strata 
  analagous 
  to 
  those 
  at 
  the 
  south 
  end 
  of 
  Puebla 
  range. 
  To 
  the 
  north- 
  

   west 
  was 
  a 
  higli 
  range, 
  presenting 
  a 
  steep 
  escarpment 
  to 
  the 
  southwest, 
  the 
  top 
  forming 
  

   a 
  table 
  land, 
  with 
  a 
  gradual 
  slope 
  to 
  tlie 
  north. 
  Siill 
  farther 
  to 
  the 
  north 
  is 
  the 
  high 
  

   range 
  of 
  Stein's 
  mountain, 
  on 
  the 
  top 
  of 
  which, 
  I 
  am 
  informed, 
  a 
  large 
  table 
  land 
  is 
  

   found. 
  

  

  