﻿84 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  mudrock 
  is 
  the 
  result 
  of 
  the 
  grinding 
  up 
  of 
  the 
  black 
  Georgian 
  

   shale 
  and 
  of 
  Snake 
  Hill 
  and 
  Normanskill 
  shales 
  on 
  both 
  sides 
  of 
  

   the 
  thrust 
  fault. 
  

  

  Tornebohm 
  (1896) 
  has 
  first 
  shown 
  how 
  the 
  rocks 
  are 
  ground 
  

   into 
  flour 
  along 
  the 
  great 
  overthrust 
  planes. 
  He 
  terms 
  this 
  flour 
  

   " 
  Friktionsbrei 
  " 
  (mylonite) 
  stating 
  that 
  it 
  served 
  as 
  " 
  Schmier- 
  

   mittel 
  " 
  (lubricating 
  substance) 
  during 
  the 
  overthrusting 
  and 
  that 
  

   its 
  thickness 
  depends 
  on 
  the 
  obstacles 
  in 
  the 
  mass 
  that 
  is 
  overridden. 
  

   In 
  the 
  French 
  central 
  plateau 
  these 
  masses 
  are 
  said 
  to 
  reach 
  several 
  

   hundred 
  meters 
  in 
  thickness. 
  

  

  That 
  in 
  Bald 
  mountain 
  the 
  conditions 
  that 
  rest 
  in 
  the 
  resistance 
  

   of 
  the 
  underground 
  were 
  especially 
  favorable 
  for 
  the 
  accumula- 
  

   tion 
  of 
  the 
  mylonite, 
  is 
  distinctly 
  shown 
  by 
  the 
  bulging 
  up 
  of 
  the 
  

   Bald 
  mountain 
  limestone 
  mass 
  there, 
  the 
  limestone, 
  together 
  with 
  

   the 
  overlying 
  Georgian 
  rocks, 
  descending 
  north 
  and 
  south 
  of 
  the 
  

   face 
  of 
  the 
  Bald 
  mountain 
  quarry, 
  away 
  from 
  the 
  mountain. 
  

  

  THE 
  NORMANSKILL 
  SHALE 
  

  

  This 
  graptolite 
  shale 
  which 
  has 
  received 
  its 
  name 
  from 
  the 
  ex- 
  

   posure 
  at 
  the 
  Normans 
  kill 
  at 
  Albany, 
  forms 
  two 
  belts 
  on 
  the 
  

   Schuylerville 
  quadrangle, 
  one, 
  entirely 
  surrounded 
  by 
  Snake 
  Hill 
  

   beds, 
  coming 
  up 
  from 
  the 
  Cohoes 
  quadrangle 
  and 
  terminating 
  near 
  

   the 
  mouth 
  of 
  the 
  Batten 
  kill, 
  and 
  another 
  south 
  of 
  the 
  Georgian 
  

   overthrust 
  mass, 
  culminating 
  in 
  Willard 
  mountain. 
  

  

  As 
  in 
  the 
  entire 
  shale 
  belt 
  in 
  the 
  Hudson 
  River 
  valley, 
  the 
  

   greater 
  part 
  of 
  the 
  Normanskill 
  formation 
  consists 
  of 
  blue 
  to 
  

   gray, 
  mostly 
  argillaceous, 
  often 
  more 
  or 
  less 
  sandy 
  shales, 
  with 
  

   thin 
  intercalations 
  of 
  black, 
  highly 
  carbonaceous 
  graptolitiferous 
  

   and 
  frequently 
  pyritif 
  erous 
  shales 
  ; 
  the 
  lighter 
  bluish 
  gray 
  and 
  black 
  

   shales 
  often 
  giving 
  the 
  rock 
  a 
  banded 
  appearance 
  in 
  the 
  common 
  

   edgewise 
  view. 
  

  

  Where 
  these 
  shales 
  are 
  brought 
  up 
  from 
  such 
  depths 
  that 
  they 
  

   are 
  still 
  fresh 
  and 
  unaffected 
  by 
  surface 
  weathering 
  and 
  frost, 
  

   they 
  appear 
  quite 
  different, 
  as 
  more 
  or 
  less 
  compact 
  bluish 
  gray 
  

   and 
  black 
  mudrocks. 
  Considerable 
  material 
  of 
  this 
  character 
  was 
  

   seen 
  at 
  the 
  new 
  canal 
  locks 
  above 
  Schuylerville 
  and 
  in 
  other 
  places. 
  

  

  The 
  shales 
  of 
  the 
  Normanskill 
  formation 
  include, 
  however, 
  two 
  

   other 
  kinds 
  of 
  rock 
  in 
  such 
  quantities 
  that 
  their 
  frequent 
  appear- 
  

   ance 
  in 
  outcrops 
  can 
  be 
  considered 
  as 
  quite 
  characteristic 
  of 
  the 
  

   formation. 
  These 
  are 
  the 
  " 
  white 
  weathering 
  cherty 
  beds 
  " 
  and 
  

   the 
  grit. 
  

  

  