﻿GEOLOGIC 
  FORMATIONS 
  OF 
  NEW 
  YORK 
  173 
  

  

  pods 
  were 
  represented 
  in 
  great 
  development 
  by 
  the 
  orthoceras 
  

   in 
  the 
  Lower 
  Silurian 
  seas, 
  so 
  were 
  they 
  represented 
  by 
  the 
  am- 
  

   monite 
  in 
  the 
  Jurassic. 
  The 
  orthoceras 
  disappeared 
  after 
  the 
  

   Triassic 
  age. 
  

  

  The 
  smaller 
  mollusks 
  were 
  also 
  abundant 
  and 
  began 
  to 
  assume 
  

   more 
  nearly 
  the 
  features 
  of 
  those 
  which 
  occur 
  at 
  the 
  present 
  day. 
  

   At 
  this 
  time 
  the 
  oyster 
  made 
  its 
  appearance. 
  

  

  CKETACEOUS 
  SYSTEM 
  

  

  The 
  Jurassic 
  system 
  was 
  succeeded 
  by 
  the 
  Cretaceous. 
  This 
  

   received 
  its 
  name 
  in 
  Europe 
  from 
  the 
  chalk 
  formation, 
  which 
  in 
  

   England 
  and 
  France 
  is 
  very 
  prominent, 
  being 
  several 
  hun- 
  

   dred 
  feet 
  thick. 
  The 
  chalk 
  is 
  a 
  limestone 
  which 
  has 
  not 
  been 
  

   consolidated. 
  If 
  it 
  had 
  been 
  exposed 
  to 
  the 
  same 
  agencies 
  as 
  

   the 
  Palaeozoic 
  limestones 
  it 
  would 
  probably 
  like 
  them 
  have 
  been 
  

   consolidated 
  to 
  form 
  a 
  hard 
  rock. 
  A 
  large 
  part 
  of 
  the 
  chalk 
  

   consists 
  of 
  skeletons 
  and 
  shells 
  of 
  foraminifera, 
  some 
  of 
  the 
  

   species 
  being 
  found 
  in 
  the 
  ocean 
  at 
  the 
  present 
  day. 
  With 
  these 
  

   foraminifera, 
  which 
  are 
  mostlv 
  calcareous, 
  are 
  the 
  remains 
  of 
  other 
  

   minute 
  animals 
  called 
  polycystines 
  which 
  are 
  silicious 
  and 
  also 
  

   the 
  spicules 
  of 
  sponges. 
  These, 
  by 
  some 
  chemical 
  action, 
  have 
  

   been 
  gathered 
  together 
  and 
  consolidated 
  into 
  nodules 
  of 
  flint 
  

   which 
  is 
  a 
  variety 
  of 
  quartz 
  similar 
  in 
  composition 
  to 
  the 
  horn- 
  

   stone 
  of 
  the 
  Corniferous 
  and 
  other 
  limestones. 
  Hornstone 
  is 
  also 
  

   called 
  chert 
  and 
  has 
  furnished 
  the 
  material 
  for 
  most 
  of 
  the 
  North 
  

   American 
  Indian 
  arrow-heads 
  which 
  are 
  commonly 
  called 
  flint 
  

   arrow-heads. 
  As 
  a 
  matter 
  of 
  fact 
  the 
  true 
  flint 
  does 
  not 
  occur 
  

   in 
  America 
  and 
  technically 
  American 
  flint 
  arrow-heads 
  are 
  

   made 
  of 
  chert 
  or 
  hornstone. 
  It 
  is 
  not 
  impossible, 
  however, 
  that 
  

   early 
  traders 
  from 
  England 
  may 
  have 
  supplied 
  our 
  Indians 
  with 
  

   flint 
  from 
  Europe. 
  

  

  In 
  America 
  there 
  is 
  but 
  little 
  chalk, 
  although 
  the 
  Cretaceous 
  

   system 
  is 
  largely 
  developed. 
  It 
  extends 
  from 
  the 
  Gulf 
  of 
  Mexico 
  

   to 
  the 
  Arctic 
  ocean 
  in 
  a 
  belt 
  200 
  miles 
  wide. 
  On 
  the 
  Atlantic 
  

   coast 
  Cretaceous 
  deposits 
  are 
  found 
  beneath 
  the 
  Tertiary 
  and 
  

   consist 
  chiefly 
  of 
  sand 
  and 
  clay. 
  The 
  clays 
  which 
  occur 
  on 
  Long 
  

  

  