﻿ADIRONDACK 
  MAGNETIC 
  IRON 
  ORES 
  IO, 
  

  

  and 
  crushing 
  have 
  been 
  carried 
  to 
  an 
  extreme, 
  the 
  resultant 
  gneisses 
  

   present 
  most 
  difficult 
  problems 
  to 
  the 
  geologist 
  since 
  they 
  are 
  

   often 
  inextricably 
  involved 
  with 
  the 
  sedimentary 
  gneisses. 
  

  

  The 
  age 
  of 
  the 
  granite 
  intrusions 
  relative 
  to 
  that 
  of 
  the 
  other 
  

   igneous 
  rocks 
  has 
  been 
  demonstrated 
  in 
  only 
  a 
  few 
  cases. 
  There 
  

   is 
  little 
  question 
  that 
  some 
  granites 
  are 
  later 
  than 
  the 
  anortho- 
  

   site 
  and 
  according 
  to 
  Professor 
  Cushing 
  even 
  later 
  than 
  the 
  syen- 
  

   ite. 
  Not 
  improbably 
  they 
  may 
  represent 
  more 
  than 
  one 
  period 
  of 
  

   intrusion. 
  

  

  Dike 
  rocks. 
  The 
  dike 
  rocks 
  in 
  the 
  Adirondack 
  region 
  are 
  mostly 
  

   diabases. 
  These 
  are 
  common 
  in 
  Clinton 
  county, 
  where 
  they 
  have 
  

   been 
  uncovered 
  in 
  large 
  numbers 
  in 
  the 
  mines, 
  and 
  to 
  a 
  lesser 
  

   extent 
  in 
  Essex 
  county. 
  In 
  the 
  interior 
  and 
  on 
  the 
  southern 
  and 
  

   western 
  sides 
  they 
  occur 
  only 
  rarely. 
  The 
  dikes 
  seldom 
  attain 
  a 
  

   thickness 
  of 
  more 
  than 
  20 
  or 
  30 
  feet, 
  the 
  majority 
  perhaps 
  being 
  

   less 
  than 
  10 
  feet. 
  A 
  few 
  dikes 
  of 
  syenite 
  porphyry 
  have 
  been 
  found 
  

   in 
  Essex 
  and 
  Clinton 
  counties. 
  The 
  dikes 
  cut 
  all 
  the 
  formations 
  

   previously 
  described, 
  but 
  have 
  not 
  been 
  found 
  anywhere 
  to 
  inter- 
  

   sect 
  the 
  Paleozoic 
  strata. 
  They 
  belong 
  thus 
  to 
  the 
  Precambric. 
  

   That 
  they 
  must 
  have 
  been 
  intruded 
  very 
  late 
  in 
  Precambric 
  time 
  

   is 
  indicated 
  by 
  the 
  fact 
  that 
  they 
  have 
  undergone 
  no 
  appreciable 
  

   metamorphism 
  or 
  compression 
  in 
  which 
  the 
  other 
  crystalline 
  rocks 
  

   have 
  participated. 
  

  

  Paleozoic 
  sediments. 
  The 
  Paleozoic 
  sedimentary 
  strata, 
  which 
  

   are 
  found 
  on 
  the 
  edges 
  and 
  to 
  a 
  lesser 
  extent 
  in 
  the 
  interior 
  of 
  the 
  

   Adirondacks, 
  rest 
  in 
  nearly 
  horizontal 
  position 
  upon 
  the 
  eroded 
  

   surface 
  of 
  the 
  crystallines. 
  During 
  the 
  period 
  of 
  their 
  deposition 
  

   the 
  region 
  underwent 
  a 
  gradual 
  subsidence 
  that 
  brought 
  a 
  contin- 
  

   ually 
  increasing 
  area, 
  with 
  the 
  progress 
  of 
  time, 
  below 
  the 
  level 
  of 
  

   the 
  sea. 
  The 
  formations 
  have 
  at 
  their 
  base 
  the 
  Potsdam 
  sand- 
  

   stone, 
  while 
  the 
  highest 
  member 
  is 
  the 
  Utica 
  slate. 
  

  

  The 
  Potsdam 
  is 
  mostly 
  an 
  indurated 
  sandstone 
  or 
  quartzite, 
  

   coarse 
  and 
  conglomeratic 
  near 
  the 
  bottom. 
  It 
  lies 
  along 
  the 
  entire 
  

   northern 
  border 
  but 
  thins 
  out 
  nearly 
  to 
  disappearance 
  to 
  the 
  south. 
  

   The 
  Beekmantown, 
  or 
  Calciferous, 
  formation 
  following 
  the 
  Pots- 
  

   dam 
  consists 
  of 
  calcareous 
  sandstone 
  and 
  limestone 
  and 
  is 
  found 
  

   on 
  all 
  sides 
  except 
  the 
  western. 
  In 
  the 
  Champlain 
  region 
  it 
  attains 
  

   its 
  extreme 
  thickness. 
  The 
  Chazy 
  limestone, 
  which 
  is 
  next 
  in 
  order, 
  

   is 
  confined 
  to 
  the 
  Champlain 
  valley. 
  The 
  Lowville, 
  Black 
  River 
  

   and 
  Trenton 
  formations 
  are 
  made 
  up 
  of 
  gray 
  and 
  black 
  limestones, 
  

   with 
  shaly 
  partings 
  in 
  the 
  Trenton 
  marking 
  a 
  transition 
  into 
  the 
  

   Utica^shale, 
  the 
  last 
  of 
  the 
  series. 
  They 
  are 
  mainly 
  developed 
  on 
  

   the 
  south. 
  

  

  