﻿GEOLOGIC 
  FOKMATIONS 
  OF 
  NEW 
  YORK 
  139 
  

  

  in 
  the 
  gorge 
  of 
  the 
  Mohawk 
  protruding 
  through 
  the 
  Hudson 
  

   river 
  shale 
  and 
  Trenton 
  limestone. 
  

  

  Beneath 
  the 
  metamorphic 
  rocks 
  of 
  the 
  Archaean 
  and 
  intersect- 
  

   ing 
  them, 
  are 
  found 
  what 
  are 
  known 
  as 
  Plutonic* 
  rocks, 
  the 
  pe- 
  

   culiarity 
  of 
  which 
  is, 
  that 
  they 
  are 
  not 
  found 
  in 
  layers 
  or 
  strata, 
  

   but 
  in 
  solid 
  masses, 
  and 
  appear 
  to 
  have 
  been 
  forced 
  up 
  from 
  

   below 
  in 
  a 
  plastic 
  condition. 
  They 
  form 
  the 
  central 
  mass 
  of 
  

   the 
  Adirondacks, 
  and 
  large 
  areas 
  of 
  them 
  are 
  found 
  in 
  the 
  High- 
  

   lands 
  and 
  in 
  many 
  parts 
  of 
  New 
  England. 
  They 
  were 
  once 
  gen- 
  

   erally 
  called 
  ^ 
  primary 
  ' 
  or 
  ^ 
  primitive 
  ', 
  as 
  it 
  was 
  believed 
  that 
  

   they 
  were 
  the 
  original 
  crust 
  of 
  the 
  earth, 
  first 
  formed 
  in 
  the 
  cool- 
  

   ing 
  of 
  its 
  melted 
  mass, 
  but 
  it 
  is 
  now 
  doubted 
  whether, 
  if 
  such 
  a 
  

   crust 
  exists, 
  it 
  can 
  be 
  identified, 
  and 
  many 
  geologists 
  think 
  that 
  

   most 
  of 
  the 
  granites 
  and 
  other 
  plutonic 
  rocks 
  are 
  only 
  re-melted 
  

   and 
  altered 
  forms 
  of 
  older 
  ones. 
  That 
  many 
  such 
  masses 
  are 
  

   ®o, 
  is 
  certain; 
  and 
  whether 
  we 
  can 
  find 
  any 
  which 
  are 
  portions 
  

   of 
  an 
  original 
  crust 
  of 
  the 
  globe, 
  is 
  at 
  least 
  very 
  doubtful. 
  

  

  Containing 
  no 
  fossils, 
  these 
  rocks 
  have 
  their 
  chief 
  interest 
  in 
  

   their 
  value 
  for 
  economic 
  uses 
  in 
  building 
  and 
  other 
  purposes, 
  

   and 
  in 
  the 
  cabinet 
  specimens 
  of 
  the 
  minerals 
  which 
  they 
  so 
  often 
  

   contain. 
  

  

  The 
  Archaean 
  rocks 
  cover 
  two 
  separate 
  tracts 
  of 
  country 
  in 
  

   this 
  state, 
  one 
  in 
  its 
  southeastern 
  part 
  known 
  as 
  the 
  Highlands; 
  

   the 
  other 
  lying 
  in 
  the 
  central 
  portion 
  of 
  the 
  great 
  Adirondack 
  

   wilderness. 
  

  

  Various 
  kinds 
  of 
  rocks 
  are 
  mingled 
  over 
  most 
  of 
  these 
  

   areas, 
  seeming 
  often 
  to 
  change 
  or 
  gradually 
  pass 
  into 
  each 
  other. 
  

   The 
  metamorphic 
  masses 
  of 
  gneiss, 
  etc. 
  are 
  more 
  fully 
  exposed 
  

   (as 
  a 
  general 
  rule) 
  around 
  the 
  edges 
  of 
  the 
  tracts, 
  where 
  they 
  

   pass 
  under 
  the 
  lower 
  strata 
  of 
  foissiliferous 
  rocks; 
  while 
  the 
  

   granite, 
  hypersthene 
  and 
  other 
  plutonic 
  masses 
  are 
  more 
  fully 
  

   developed 
  near 
  the 
  centers 
  of 
  these 
  areas 
  and 
  among 
  the 
  highest 
  

   of 
  the 
  mountains. 
  

  

  Throughout 
  the 
  Archaean 
  districts 
  there 
  are 
  many 
  dykes, 
  or 
  

   veins 
  of 
  trap 
  or 
  other 
  igneous 
  rock 
  penetrating 
  masses 
  of 
  a 
  dif- 
  

   ferent 
  character. 
  Not 
  infrequently, 
  a 
  mountain 
  or 
  hill 
  shows 
  

  

  a 
  Plutonic, 
  from 
  Pluto, 
  king 
  of 
  the 
  infernal 
  regions 
  in 
  Pagan 
  mythology. 
  

  

  