﻿54 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  quite 
  so 
  prominently 
  of 
  this 
  type 
  as 
  in 
  the 
  case 
  of 
  the 
  corresponding 
  

   rocks 
  of 
  the 
  central 
  and 
  eastern 
  Adirondacks. 
  We 
  are 
  forced 
  to 
  

   argue 
  that, 
  when 
  these 
  rocks 
  were 
  deformed, 
  a 
  considerable 
  thick- 
  

   ness 
  of 
  other 
  rock 
  overlay 
  them, 
  which 
  thickness 
  was 
  subsequently 
  

   worn 
  away. 
  This 
  surface 
  wear 
  goes 
  on 
  very 
  slowly 
  at 
  best, 
  and 
  

   must 
  have 
  been 
  continued 
  through 
  long 
  ages, 
  yet 
  was 
  completed 
  

   before 
  Potsdam 
  deposition 
  began. 
  The 
  time 
  involved 
  is 
  many 
  mil- 
  

   lions 
  of 
  years, 
  in 
  all 
  probabihty 
  a 
  rock 
  thickness 
  of 
  at 
  least 
  a 
  mile 
  

   or 
  two 
  was 
  removed, 
  and 
  yet 
  at 
  the 
  close 
  the 
  region 
  was 
  pared 
  

   down 
  to 
  a 
  surface 
  of 
  comparative 
  smoothness. 
  Much 
  Grenville 
  

   has 
  thus 
  disappeared, 
  the 
  tops 
  of 
  the 
  igneous 
  bathyliths 
  are 
  gone, 
  

   together 
  with 
  whatever 
  of 
  younger 
  rocks 
  may 
  have 
  been 
  present 
  

   above 
  them. 
  The 
  diabases 
  were 
  intruded 
  toward 
  the 
  close 
  of 
  this 
  

   long 
  period, 
  since 
  plainly 
  they 
  solidified 
  not 
  far 
  beneath 
  the 
  surface. 
  

  

  PALEOZOIC 
  ROCKS 
  1 
  

  

  The 
  Paleozoic 
  rocks 
  of 
  the 
  district, 
  for 
  mapping 
  purposes 
  on 
  

   maps 
  of 
  this 
  scale, 
  are 
  separable 
  into 
  six 
  quite 
  distinct 
  lithologic 
  

   units, 
  which 
  in 
  large 
  part 
  coincide 
  with 
  the 
  subdivisions 
  of 
  these 
  

   rocks 
  made 
  long 
  ago 
  by 
  the 
  early 
  geologists 
  of 
  the 
  State. 
  These 
  

   are, 
  in 
  order 
  of 
  age 
  from 
  below 
  upwards, 
  the 
  Potsdam 
  sandstone, 
  

   Theresa 
  dolomite, 
  Pamelia 
  limestone, 
  and 
  Lowville, 
  Black 
  River 
  

   and 
  Trenton 
  limestones. 
  Above 
  the 
  last 
  named 
  the 
  Utica 
  and 
  Lor- 
  

   raine 
  shales 
  come 
  in, 
  but 
  these 
  nowhere 
  reach 
  the 
  map 
  limits, 
  their 
  

   northerly 
  boundaries 
  being 
  found 
  on 
  the 
  Watertown 
  and 
  Sacketts 
  

   Harbor 
  sheets, 
  next 
  south. 
  

  

  The 
  basal 
  member 
  of 
  this 
  sedimentary 
  series, 
  the 
  Potsdam 
  sand- 
  

   stone, 
  was 
  deposited 
  upon 
  the 
  worn 
  surface 
  of 
  the 
  Precambric 
  

   rocks, 
  and 
  in 
  order 
  to 
  properly 
  describe 
  the 
  sandstone 
  it 
  is 
  neces- 
  

   sary 
  to 
  present 
  in 
  some 
  detail 
  the 
  character 
  of 
  this 
  surface. 
  

  

  Precambric 
  surface 
  underneath 
  the 
  Potsdam 
  

  

  That 
  the 
  surface 
  on 
  which 
  the 
  Potsdam 
  sandstone 
  was 
  laid 
  down 
  

   was 
  far 
  from 
  being 
  an 
  even 
  one 
  was 
  clearly 
  stated 
  by 
  Smyth, 
  in 
  his 
  

   report 
  on 
  the 
  district.- 
  

  

  That 
  a 
  similar 
  irregular 
  floor 
  is 
  present 
  in 
  many 
  parts 
  of 
  Canada, 
  

   of 
  the 
  upper 
  lake 
  region 
  and 
  of 
  northern 
  New 
  York, 
  has 
  been 
  shown 
  

   by 
  many 
  observers. 
  There 
  is 
  therefore 
  nothing 
  novel 
  in 
  the 
  features 
  

   to 
  be 
  described, 
  but 
  they 
  are 
  worthy 
  of 
  somewhat 
  extended 
  descrip- 
  

  

  1 
  By 
  H. 
  P. 
  Gushing. 
  

  

  2 
  N. 
  Y. 
  State 
  Geol. 
  19th 
  An. 
  Rep't, 
  p. 
  rioo-i. 
  

  

  