﻿8 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  single 
  area 
  of 
  the 
  sort 
  appears 
  in 
  the 
  southeast 
  part 
  of 
  the 
  

   Theresa 
  sheet, 
  on 
  which 
  is 
  found 
  the 
  western 
  portion 
  of 
  the 
  

   '' 
  sand 
  plains," 
  the 
  great 
  Pleistocene 
  delta 
  of 
  the 
  Black 
  river. 
  

  

  Interesting 
  historically 
  from 
  having 
  been 
  the 
  scene 
  of 
  exploita- 
  

   tion 
  and 
  settlement 
  by 
  French 
  immigrants 
  of 
  high 
  class, 
  during 
  

   the 
  early 
  part 
  of 
  the 
  nineteenth 
  century, 
  the 
  district 
  preserves 
  

   many 
  traces 
  of 
  this 
  immigration, 
  especially 
  in 
  the 
  m.atter 
  of 
  

   geographic 
  nomenclature. 
  

  

  SUMMARY 
  OF 
  GEOLOGIC 
  HISTORY 
  ^ 
  

  

  The 
  rocks 
  of 
  the 
  region 
  are 
  readily 
  separable 
  into 
  two 
  great 
  

   groups, 
  the 
  one 
  of 
  older 
  crystalline 
  rocks, 
  and 
  the 
  other 
  ot 
  

   younger 
  sandstones, 
  limestones 
  and 
  shales 
  which 
  rest 
  upon 
  the 
  

   older 
  group. 
  The 
  rocks 
  of 
  the 
  older 
  group 
  are 
  of 
  Precambric 
  

   age, 
  are 
  among 
  the 
  most 
  ancient 
  rocks 
  of 
  which 
  we 
  anywhere 
  

   have 
  knowledge, 
  and 
  are 
  in 
  most 
  respects 
  identical 
  with 
  the 
  

   crystalline 
  rocks 
  which 
  compose 
  the 
  great 
  central 
  region 
  of 
  

   northern 
  New 
  York, 
  the 
  Adirondack 
  region, 
  and 
  with 
  those 
  of 
  

   the 
  much 
  more 
  extensive 
  area 
  Avhich 
  lies 
  to 
  the 
  northward 
  in 
  

   Canada. 
  These 
  rocks, 
  in 
  the 
  district 
  here 
  reported 
  upon, 
  form 
  

   a 
  narrow 
  connecting 
  link, 
  or 
  isthmus, 
  between 
  the 
  exposures 
  of 
  

   these 
  two 
  areas, 
  Avhich 
  otherwise 
  are 
  completely 
  separated 
  

   from 
  one 
  another 
  by 
  a 
  belt 
  of 
  country 
  of 
  considerable 
  width 
  in 
  

   which 
  the 
  surface 
  rocks 
  belong 
  to 
  the 
  younger 
  group. 
  It 
  is 
  

   only 
  in 
  the 
  immediate 
  region 
  therefore 
  that 
  direct 
  connection 
  

   can 
  be 
  traced 
  between 
  the 
  old 
  rocks 
  of 
  Canada 
  and 
  of 
  New 
  

   York, 
  and 
  this 
  fact 
  gives 
  added 
  interest 
  to 
  the 
  study 
  of 
  these 
  

   rocks 
  here. 
  

  

  These 
  Precambric 
  recks 
  furnish 
  us 
  with 
  our 
  most 
  ancient 
  direct 
  

   records 
  of 
  the 
  history 
  of 
  the 
  earth, 
  but 
  like 
  most 
  ancient 
  records 
  

   they 
  are 
  fragmentary 
  and 
  difficult 
  to 
  decipher. 
  Nevertheless 
  they 
  

   plainly 
  indicate 
  that 
  Precambric 
  time 
  was 
  of 
  enormous 
  duration, 
  

   involving 
  many 
  millions 
  of 
  years. 
  

  

  Here, 
  as 
  elsewhere 
  in 
  northern 
  New 
  York, 
  these 
  rocks 
  consist 
  

   of 
  but 
  a 
  single 
  series 
  of 
  water-deposited 
  rocks, 
  so 
  far 
  as 
  our 
  

   knowledge 
  goes. 
  This 
  is 
  known 
  as 
  the 
  Grenville 
  series, 
  and 
  

   comprises 
  rocks 
  which, 
  originally 
  deposited 
  as 
  shales, 
  limestones, 
  and 
  

   sandstones, 
  are 
  now 
  greatly 
  changed 
  in 
  character 
  and 
  have 
  become 
  

   white, 
  coarsely 
  crystalline 
  limestones, 
  glassy 
  quartzites, 
  and 
  schists 
  

   and 
  gneisses 
  of 
  many 
  varieties. 
  Curiously 
  we 
  have 
  not 
  as 
  yet, 
  in 
  

  

  1 
  By 
  H. 
  P. 
  Gushing. 
  This 
  is 
  a 
  simple 
  statement 
  of 
  the 
  outlines 
  of 
  the 
  

   history 
  of 
  the 
  region 
  as 
  disclosed 
  by 
  the 
  study 
  of 
  the 
  district. 
  The 
  detailed 
  

   evidence 
  upon 
  which 
  these 
  statements 
  are 
  based, 
  will 
  follow 
  later. 
  

  

  