﻿GEOLOGY 
  OF 
  SARATOGA 
  SPRINGS 
  AND 
  VICINITY 
  115 
  

  

  and 
  which 
  is 
  the 
  cause 
  of 
  the 
  Appalachian 
  and 
  Green 
  Mountain- 
  

   Taconic 
  fold 
  systems 
  but 
  which 
  also, 
  as 
  Ulrich 
  lucidly 
  shows, 
  causes 
  

   contraction 
  of 
  these 
  tracts 
  of 
  the 
  eastern 
  continental 
  coast 
  by 
  over- 
  

   thrusting, 
  where 
  deep-seated 
  buttresses, 
  as 
  the 
  Adirondacks 
  are 
  

   opposed 
  to 
  the 
  folds. 
  

  

  One 
  of 
  the 
  overthrust 
  planes 
  which 
  have 
  been 
  observed 
  on 
  the 
  

   Schuylerville 
  sheet, 
  namely, 
  that 
  separating 
  the 
  Georgian 
  rocks 
  

   from 
  the 
  underlying 
  Ordovicic 
  beds, 
  can 
  be 
  traced 
  southward 
  along 
  

   the 
  western 
  edge 
  of 
  the 
  Georgian 
  to 
  a 
  locality 
  near 
  Schodack 
  Land- 
  

   ing, 
  about 
  15 
  miles 
  south 
  of 
  Albany, 
  where 
  the 
  Georgian 
  belt 
  termi- 
  

   nates 
  near 
  the 
  Hudson. 
  It 
  is 
  now 
  an 
  interesting 
  fact 
  that 
  in 
  the 
  

   direct 
  southwestward 
  continuation 
  of 
  the 
  overthrust 
  plane 
  similar 
  

   overthrusts 
  can 
  be 
  observed 
  along 
  which 
  the 
  Siluric 
  and 
  Devonic 
  

   rocks 
  have 
  been 
  moved 
  westward. 
  Chadwick 
  has 
  described 
  such 
  a 
  

   fault 
  from 
  Saugerties, 
  1 
  about 
  30 
  miles 
  southwest 
  from 
  Schodack 
  

   Landing 
  and 
  between 
  the 
  latter 
  place 
  and 
  the 
  large 
  overthrusts 
  at 
  

   Rondout, 
  described 
  by 
  van 
  Ingen 
  and 
  Clark. 
  If 
  these 
  overthrusts 
  

   all 
  belong 
  to 
  the 
  same 
  orogenic 
  movement, 
  the 
  latter 
  is 
  at 
  least 
  of 
  

   post-Devonic 
  age 
  and 
  probably 
  dates, 
  like 
  all 
  the 
  typical 
  Appa- 
  

   lachian 
  orogenic 
  movements, 
  from 
  the 
  close 
  of 
  the 
  Paleozoic 
  era, 
  

   or 
  is 
  still 
  younger. 
  

  

  THE 
  NORTHUMBERLAND 
  VOLCANIC 
  PLUG 
  

   BY 
  H. 
  P. 
  CUSHING 
  

  

  One 
  mile 
  north 
  of 
  the 
  village 
  of 
  Schuylerville, 
  near 
  the 
  Hudson 
  

   river, 
  is 
  a 
  knob 
  of 
  volcanic 
  or 
  effusive 
  rock 
  of 
  quite 
  exceptional 
  

   occurrence. 
  Woodworth 
  was 
  the 
  first 
  geologist 
  to 
  recognize 
  its 
  

   true 
  nature 
  and 
  to 
  describe 
  it. 
  2 
  Since 
  1901, 
  when 
  his 
  study 
  was 
  

   made, 
  a 
  considerable 
  part 
  of 
  the 
  knob 
  has 
  been 
  quarried 
  away 
  for 
  

   road 
  metal 
  and 
  other 
  purposes, 
  exposing 
  many 
  features 
  of 
  the 
  

   occurrence 
  which 
  were 
  not 
  originally 
  visible, 
  and 
  also 
  furnishing 
  

   comparatively 
  fresh 
  rock 
  for 
  chemical 
  study. 
  The 
  reader 
  can 
  

   obtain 
  some 
  conception 
  of 
  the 
  differences 
  between 
  the 
  knob 
  as 
  seen 
  

   in 
  1901 
  and 
  as 
  it 
  was 
  ten 
  years 
  later 
  by 
  comparing 
  plates 
  17 
  and 
  18. 
  

  

  Woodworth 
  proposed 
  the 
  name 
  of 
  Stark's 
  knob 
  for 
  this 
  hill. 
  

   The 
  name 
  is 
  a 
  convenient 
  one, 
  and 
  will 
  be 
  here 
  used 
  in 
  referring 
  

   to 
  it. 
  Since 
  the 
  appearance 
  of 
  his 
  report, 
  Schuylerville 
  people 
  

   speak 
  of 
  it 
  as 
  " 
  The 
  volcano." 
  

  

  1 
  G. 
  H. 
  Chadwick. 
  Downward 
  Overthust 
  Fault 
  at 
  Saugerties. 
  N. 
  Y. 
  

   N. 
  Y. 
  State 
  Mus. 
  Bui. 
  140, 
  p. 
  157. 
  

   2 
  N. 
  Y. 
  State 
  Geol. 
  21st 
  Rept, 
  1901, 
  p. 
  rij-24. 
  

  

  