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  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Life 
  of 
  the 
  Cambrian 
  

  

  So 
  far 
  as 
  we 
  know, 
  the 
  life 
  of 
  the 
  Cambrian 
  was 
  wholly 
  marine. 
  

   No 
  vertebrates 
  are 
  known 
  to 
  have 
  existed. 
  The 
  Brachiopods 
  

   were 
  small. 
  The 
  Lamellibranchs, 
  so 
  far 
  as 
  known, 
  were 
  also 
  very 
  

   small. 
  There 
  were 
  representatives 
  of 
  the 
  groups 
  of 
  Pteropods 
  

   and 
  Gastropods. 
  Cephalopods 
  appeared 
  in 
  the 
  Upper 
  Cambrian. 
  

   There 
  were 
  also 
  sponges, 
  and 
  corals. 
  The 
  trllobites, 
  however, 
  

   were 
  the 
  only 
  forms 
  which 
  had 
  attained 
  large 
  size 
  or 
  high 
  de- 
  

   velopment. 
  Besides 
  these 
  were 
  some 
  other 
  articulates_, 
  the 
  

   Ostracoids 
  and 
  Phyllopods, 
  and 
  probably 
  some 
  worms. 
  The 
  

   plants 
  were 
  sea 
  weeds. 
  

  

  LOWER 
  SILURIAN 
  OR 
  ORDOVICIAN 
  

  

  This 
  system 
  is 
  a 
  subdivision 
  of 
  the 
  original 
  Silurian 
  system 
  

   which 
  received 
  its 
  name 
  from 
  that 
  of 
  the 
  Silures, 
  an 
  ancient 
  race 
  

   inhabiting 
  the 
  eastern 
  part 
  of 
  Wales, 
  where 
  Sir 
  Roderick. 
  Mur- 
  

   chison 
  studied 
  these 
  rocks 
  in 
  detail. 
  The 
  second 
  name 
  was 
  de- 
  

   rived 
  by 
  the 
  British 
  geologist 
  Lapworth 
  from 
  that 
  of 
  the 
  Ordo- 
  

   vices, 
  also 
  an 
  ancient 
  British 
  tribe. 
  

  

  In 
  New 
  York 
  this 
  system 
  is 
  well 
  developed 
  and 
  includes 
  the 
  

   following 
  subdivisions: 
  

  

  System 
  Group 
  Stage 
  

  

  ( 
  Hudson 
  river 
  shale 
  and 
  sandstone 
  

   [' 
  Hudson 
  river 
  < 
  

   ' 
  ( 
  Utica 
  slate 
  

  

  f 
  Trenton 
  

   Lower 
  Silurian 
  { 
  rr 
  4 
  j 
  Black 
  river 
  

  

  I 
  Birdseye 
  

   I 
  Cliazy 
  

  

  I 
  Calciferous 
  

  

  Calciferous 
  Group 
  

  

  Overlying 
  the 
  Upper 
  Cambrian 
  or 
  Potsdam 
  sandstone 
  at 
  many 
  

   points 
  is 
  another, 
  which 
  contains 
  a 
  considerable 
  proportion 
  of 
  

   lime 
  mingled 
  with 
  it, 
  and 
  from 
  this 
  fact 
  has 
  received 
  the 
  name 
  of 
  

   the 
  Calciferous 
  sandrock. 
  

  

  It 
  may 
  be 
  described 
  as 
  a 
  silicious 
  or 
  gritty 
  limestone, 
  generally 
  

   of 
  a 
  brownish 
  color, 
  lying 
  in 
  straight, 
  thin 
  layers, 
  and 
  attaining 
  

  

  