﻿GEOLOGY 
  OF 
  SARATOGA 
  SPRINGS 
  AND 
  VICINITY 
  20, 
  

  

  dikes 
  of 
  unmetamorphosed, 
  igneous 
  rock. 
  Their 
  greater 
  youth 
  is 
  

   shown 
  by 
  the 
  fact 
  that 
  they 
  cut 
  all 
  the 
  other 
  rocks. 
  As 
  all 
  the 
  

   other 
  rocks 
  have 
  been 
  more 
  or 
  less 
  metamorphosed, 
  and 
  these 
  have 
  

   not, 
  they 
  are 
  likely 
  considerably 
  younger. 
  They 
  are 
  found 
  in 
  all 
  

   parts 
  of 
  the 
  region 
  but 
  most 
  abundantly 
  in 
  Clinton 
  county, 
  on 
  the 
  

   extreme 
  northeast, 
  whence 
  they 
  diminish 
  in 
  number 
  to 
  the 
  south 
  

   and 
  west. 
  In 
  the 
  central 
  and 
  western 
  Adirondacks 
  they 
  are 
  com- 
  

   paratively 
  scarce. 
  On 
  the 
  extreme 
  northwest, 
  in 
  the 
  Thousand 
  

   Islands 
  region, 
  they 
  become 
  again 
  abundant. 
  They 
  are 
  older 
  than 
  

   the 
  Potsdam 
  sandstone, 
  the 
  oldest 
  Paleozoic 
  rock 
  of 
  the 
  region, 
  

   and 
  hence 
  are 
  of 
  age 
  intermediate 
  between 
  it 
  and 
  the 
  other 
  Pre- 
  

   cambric 
  rocks, 
  and 
  likely 
  of 
  late 
  Precambric 
  age. 
  

  

  There 
  are 
  two 
  chief 
  varieties 
  of 
  these 
  rocks: 
  heavy, 
  black 
  traps, 
  

   and 
  less 
  dense 
  syenite 
  rocks 
  of 
  red 
  color. 
  The 
  latter 
  have 
  been 
  

   so 
  far 
  found 
  only 
  in 
  Clinton 
  county, 
  but 
  the 
  trap 
  dikes 
  range 
  

   throughout 
  the 
  region. 
  They 
  are 
  not 
  particularly 
  abundant 
  in 
  the 
  

   Saratoga 
  region, 
  but 
  those 
  that 
  do 
  occur 
  make 
  up 
  for 
  their 
  infre- 
  

   quency 
  by 
  their 
  size. 
  The 
  usual 
  trap 
  dikes 
  of 
  the 
  region 
  range 
  

   from 
  1 
  foot 
  to 
  30 
  feet 
  in 
  thickness. 
  Most 
  of 
  those 
  near 
  Saratoga 
  

   are 
  from 
  50 
  to 
  100 
  feet 
  thick, 
  and 
  we 
  have 
  traced 
  some 
  of 
  them 
  

   for 
  several 
  miles. 
  Thus 
  the 
  dike 
  numbered 
  1 
  upon 
  the 
  Saratoga 
  

   quadrangle, 
  the 
  one 
  quarried 
  for 
  road 
  metal 
  north 
  of 
  the 
  village, 
  

   can 
  be 
  followed 
  foot 
  by 
  foot 
  for 
  2 
  miles 
  north 
  and 
  south 
  of 
  the 
  

   quarry, 
  with 
  an 
  average 
  width 
  of 
  from 
  75 
  to 
  100 
  feet. 
  To 
  the 
  

   north 
  it 
  runs 
  into 
  low, 
  swampy 
  ground 
  for 
  2 
  miles 
  but 
  beyond 
  

   that 
  and 
  precisely 
  on 
  the 
  trend 
  of 
  this 
  dike 
  we 
  have 
  repeatedly 
  

   found 
  a 
  huge 
  dike 
  of 
  the 
  same 
  width, 
  for 
  an 
  additional 
  distance 
  

   of 
  7 
  miles 
  more, 
  which 
  we 
  confidently 
  assume 
  to 
  be 
  the 
  same 
  dike. 
  

   Both 
  to 
  the 
  east 
  and 
  west 
  of 
  this 
  big 
  dike 
  are 
  others 
  which 
  fiave 
  

   been 
  traced 
  for 
  several 
  miles, 
  and 
  are 
  50 
  feet 
  or 
  more 
  in 
  width. 
  

  

  These 
  are 
  all 
  ordinary 
  diabases. 
  Olivine 
  has 
  not 
  been 
  identified 
  

   with 
  certainty 
  in 
  any 
  of 
  them. 
  They 
  are 
  labradorite, 
  augite, 
  mag- 
  

   netite 
  rocks 
  with 
  good 
  ophitic 
  structure. 
  All 
  are 
  considerably 
  

   altered. 
  It 
  is 
  exceptional 
  to 
  find 
  the 
  augite 
  in 
  fresh 
  condition, 
  and 
  

   much 
  of 
  the 
  feldspar 
  is 
  also 
  altered. 
  In 
  this 
  respect 
  the 
  dikes 
  

   show 
  sharp 
  contrast 
  with 
  those 
  of 
  the 
  northern 
  Adirondacks 
  where 
  

   the 
  larger 
  number 
  of 
  the 
  dikes 
  are 
  very 
  fresh. 
  This 
  we 
  attribute 
  

   to 
  the 
  more 
  vigorous 
  glacial 
  erosion 
  on 
  the 
  north. 
  

  

  