﻿A. 
  M. 
  Edwards 
  — 
  Infusorial 
  Earths 
  of 
  Pacific 
  Coast 
  371 
  

  

  from 
  each 
  other 
  only 
  in 
  time 
  and 
  in 
  the 
  fact 
  that 
  in 
  the 
  most 
  

   recent 
  a 
  certain 
  amount 
  of 
  organic 
  matter 
  usually 
  remains 
  and 
  

   the 
  material 
  is 
  light 
  and 
  readily 
  pulverulent. 
  We 
  have 
  in 
  the 
  

   older 
  one, 
  on 
  account 
  of 
  the 
  volcanic 
  heat 
  added 
  to, 
  or 
  with- 
  

   out 
  aqueous 
  action, 
  the 
  material 
  has 
  had 
  all 
  of 
  its 
  organic 
  mat- 
  

   ter 
  removed. 
  And 
  it 
  has 
  become 
  a 
  less 
  or 
  more 
  hard 
  rocky 
  

   mass 
  of 
  a 
  light 
  color. 
  Hence 
  we 
  have 
  strata 
  of 
  a 
  totally 
  differ- 
  

   ent 
  character. 
  These 
  are 
  of 
  marine 
  origin 
  and 
  of 
  an 
  age 
  sup- 
  

   posed 
  to 
  be 
  coincident 
  with 
  the 
  Miocene 
  Tertiary. 
  At 
  all 
  

   events 
  they 
  are 
  much 
  older 
  than 
  the 
  most 
  ancient 
  fresh 
  water 
  

   stratum 
  containing 
  Diatomacese 
  as 
  yet 
  discovered. 
  Of 
  the 
  

   mode 
  of 
  formation 
  of 
  these 
  last 
  mentioned 
  strata 
  I 
  shall 
  not 
  

   now 
  pause 
  to 
  treat, 
  as 
  I 
  have 
  already 
  thrown 
  out 
  some 
  hints 
  

   respecting 
  my 
  opinions 
  upon 
  this 
  point 
  in 
  some 
  remarks 
  made 
  

   before 
  the 
  Essex 
  Institute, 
  Salem, 
  Mass., 
  January 
  4th, 
  1869, 
  

   an 
  abstract 
  of 
  which 
  will 
  be 
  found 
  in 
  the 
  Bulletin 
  of 
  that 
  asso- 
  

   ciation, 
  vol. 
  i, 
  page 
  11. 
  I 
  have 
  treated 
  of 
  the 
  same 
  subject 
  in 
  

   a 
  paper 
  read 
  before 
  the 
  American 
  Association 
  for 
  the 
  Advance- 
  

   ment 
  of 
  Science, 
  at 
  the 
  Salem 
  meeting, 
  August 
  25th, 
  1869. 
  

   Hereafter 
  I 
  will 
  treat 
  fully 
  of 
  this 
  subject 
  in 
  my 
  report 
  on 
  the 
  

   microscopic 
  material 
  of 
  the 
  Geological 
  Survey 
  of 
  California 
  

   now 
  in 
  preparation. 
  

  

  It 
  will 
  be 
  readily 
  perceived 
  that 
  it 
  is 
  fortunate 
  that 
  my 
  

   report 
  on 
  the 
  matter 
  herein 
  treated 
  of 
  was 
  not 
  published 
  at 
  the 
  

   time 
  it 
  was 
  sent 
  in, 
  and 
  I 
  feel 
  that 
  I 
  can 
  congratulate 
  myself 
  

   that 
  Mr. 
  Gibbs 
  has 
  again 
  submitted 
  the 
  matter 
  to 
  me 
  for 
  

   revision, 
  for 
  at 
  the 
  present 
  time 
  I 
  can 
  do 
  more 
  justice 
  to 
  it 
  and 
  

   throw 
  light 
  upon 
  some 
  points 
  which, 
  at 
  the 
  time, 
  I 
  was 
  unable 
  

   to 
  fully 
  comprehend. 
  

  

  The 
  constantly 
  recurring 
  records 
  of 
  the 
  discovery 
  of 
  fossilif- 
  

   erous 
  deposits 
  containing 
  the 
  remains 
  of 
  such 
  minute 
  organ- 
  

   isms 
  as 
  the 
  Diatomacere, 
  Radiolaria 
  and 
  Rhizopoda, 
  constitut- 
  

   ing 
  the 
  well 
  known 
  ' 
  Infusorial 
  earths 
  ' 
  of 
  most 
  geologists 
  

   reveal 
  the 
  fact 
  that 
  these 
  atomies 
  play 
  a 
  very 
  important 
  part 
  

   in 
  the 
  world's 
  future 
  ; 
  and 
  while 
  almost 
  every 
  newly 
  found 
  

   specimen 
  exhibits 
  one, 
  if 
  not 
  more, 
  of 
  what 
  have 
  been 
  consid- 
  

   ered 
  new 
  species, 
  it 
  proves, 
  at 
  the 
  same 
  time, 
  the 
  cosmopolitan 
  

   character 
  of 
  many 
  already 
  known 
  forms, 
  which 
  are 
  thus 
  seen 
  

   to 
  occur 
  spread 
  over 
  the 
  globe 
  in 
  great 
  profusion 
  from 
  the 
  

   equator 
  to 
  the 
  poles. 
  In 
  some 
  cases 
  these 
  widely-spread 
  species 
  

   will 
  not 
  vary 
  appreciably, 
  be 
  their 
  dwelling 
  place 
  under 
  the 
  

   burning 
  sun 
  of 
  the 
  tropics, 
  the 
  more 
  equable 
  climate 
  of 
  the 
  

   temperate 
  zone 
  or 
  the 
  frozen 
  fields 
  of 
  the 
  poles. 
  Other 
  forms, 
  

   however, 
  on 
  the 
  contrary, 
  appear 
  to 
  vary 
  to 
  so 
  great 
  an 
  extent 
  

   with 
  every 
  few 
  degrees 
  of 
  latitude 
  that 
  specimens 
  gathered 
  at 
  

   the 
  equator 
  and 
  in 
  localities 
  a 
  very 
  little 
  removed 
  therefrom, 
  

   either 
  north 
  or 
  south, 
  might 
  be 
  supposed, 
  on 
  superficial 
  exam 
  

  

  