﻿112 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Dikes. 
  A 
  minor 
  feature 
  of 
  the 
  geology 
  of 
  the 
  region 
  is 
  the 
  occur- 
  

   rence 
  of 
  dikes 
  which 
  are 
  specially 
  common 
  in 
  the 
  vicinity 
  of 
  the 
  

   ore 
  bodies. 
  They 
  belong 
  to 
  two 
  series 
  of 
  intrusions, 
  an 
  older 
  

   represented 
  by 
  granite 
  and 
  a 
  younger 
  consisting 
  of 
  diabase. 
  

  

  The 
  granite 
  dikes 
  vary 
  from 
  a 
  few 
  inches 
  to 
  several 
  feet 
  in 
  width. 
  

   In 
  appearance 
  they 
  resemble 
  the 
  reddish 
  gneiss, 
  from 
  which 
  they 
  

   can.be 
  distinguished, 
  however, 
  quite 
  readily 
  by 
  their 
  finer 
  and 
  more 
  

   massive 
  texture. 
  Mineralogically 
  they 
  consist 
  of 
  quartz 
  and 
  feld- 
  

   spar, 
  with 
  subordinate 
  augite, 
  magnetite, 
  titanite 
  and 
  zircon. 
  The 
  

   feldspar 
  is 
  prevailingly 
  orthoclase, 
  but 
  a 
  triclinic 
  variety, 
  probably 
  

   oligoclase, 
  is 
  usually 
  present. 
  The 
  dikes 
  are 
  almost 
  identical 
  in 
  

   composition 
  with 
  the 
  Birch 
  hill 
  granite 
  which 
  strongly 
  points 
  to 
  

   the 
  conclusion 
  that 
  the 
  two 
  rocks 
  are 
  genetically 
  related. 
  The 
  

   granite 
  dikes 
  can 
  be 
  best 
  observed 
  at 
  the 
  Williams 
  and 
  Burden 
  

   openings. 
  At 
  the 
  former 
  locality 
  there 
  are 
  several 
  running 
  paral- 
  

   lel 
  to 
  or 
  slightly 
  diverging 
  from 
  the 
  course 
  of 
  the 
  ore 
  body. 
  The 
  

   only 
  contact 
  effect 
  consequent 
  upon 
  the 
  intrusion 
  of 
  the 
  dikes 
  is 
  

   a 
  slightly 
  bluish 
  tint 
  assumed 
  by 
  the 
  magnetite. 
  

  

  The 
  diabase 
  dikes 
  occur 
  in 
  numbers 
  both 
  on 
  the 
  surface 
  and 
  in 
  

   the 
  underground 
  workings. 
  They 
  range 
  up 
  to 
  15 
  feet 
  thick, 
  the 
  

   largest 
  one 
  observed 
  being 
  near 
  slope 
  15. 
  They 
  do 
  not 
  follow 
  any 
  

   one 
  direction, 
  though 
  the 
  majority 
  of 
  them 
  have 
  a 
  nearly 
  east-west 
  

   strike, 
  while 
  most 
  of 
  the 
  others 
  run 
  about 
  n. 
  30 
  w. 
  New 
  dikes 
  

   are 
  frequently 
  encountered 
  in 
  the 
  course 
  of 
  the 
  mining 
  operations. 
  

  

  The 
  petrography 
  of 
  the 
  dikes 
  has 
  been 
  described 
  by 
  Kemp 
  and 
  

   Marsters, 
  1 
  who 
  state 
  that 
  they 
  are 
  all 
  diabase, 
  though 
  showing 
  

   some 
  variation 
  in 
  individual 
  cases. 
  One 
  dike 
  from 
  the 
  Hall 
  slope 
  

   is 
  said 
  to 
  be 
  characterized 
  by 
  the 
  presence 
  of 
  small 
  hornblende 
  crys- 
  

   tals 
  in 
  addition 
  to 
  those 
  of 
  augite, 
  showing 
  a 
  transition 
  to 
  camp- 
  

   tonite. 
  The 
  writer's 
  observations 
  are 
  in 
  accord 
  with 
  the 
  view 
  cited 
  

   as 
  to 
  the 
  diabase 
  nature 
  of 
  the 
  dikes. 
  With 
  one 
  or 
  two 
  exceptions 
  

   examination 
  of 
  thin 
  sections 
  revealed 
  little 
  that 
  is 
  noteworthy 
  in 
  

   their 
  composition 
  or 
  texture. 
  A 
  small 
  dike 
  from 
  slope 
  4 
  is 
  charac- 
  

   terized 
  by 
  a 
  pronounced 
  porphyritic 
  habit 
  due 
  to 
  the 
  inclusion 
  of 
  

   augite 
  phenocrysts 
  in 
  a 
  fine 
  ground 
  mass 
  of 
  augite 
  and 
  plagioclase. 
  

   Some 
  dikes 
  are 
  peculiarly 
  rich 
  in 
  magnetite 
  which 
  has 
  probably 
  

   been 
  absorbed 
  from 
  the 
  ore 
  bodies 
  during 
  the 
  period 
  of 
  intrusion. 
  

   This 
  mineral 
  frequently 
  takes 
  the 
  unusual 
  form 
  of 
  long 
  needles 
  

   which 
  are 
  arranged 
  in 
  parallel 
  groups 
  crossing 
  one 
  another 
  at 
  

  

  1 
  The 
  Trap 
  Dikes 
  of 
  the 
  Lake 
  Champlain 
  District. 
  U. 
  S. 
  Geol. 
  Sur. 
  Bui. 
  

   107. 
  1893. 
  p. 
  447-48. 
  

  

  