﻿GEOLOGY 
  OF 
  SARATOGA 
  SPRINGS 
  AND 
  VICINITY 
  

  

  123 
  

  

  fault 
  must 
  lie 
  between 
  it 
  and 
  the 
  main 
  mass 
  of 
  the 
  knob. 
  But 
  

   these 
  other 
  shale 
  wedges 
  within 
  the 
  trap 
  mass 
  suggest 
  the 
  query 
  

   whether 
  the 
  shale 
  in 
  Woodworth's 
  section 
  may 
  not 
  also 
  be 
  a 
  wedge 
  

   with 
  trap 
  beneath. 
  

  

  At 
  the 
  extreme 
  north 
  edge 
  of 
  the 
  knob 
  is 
  another 
  projecting 
  

   point, 
  remaining 
  unquarried. 
  A 
  portion 
  of 
  this 
  point 
  is 
  shown 
  at 
  

   the 
  extreme 
  right 
  in 
  plate 
  18, 
  though 
  most 
  of 
  it 
  did 
  not 
  get 
  into 
  

   the 
  view. 
  Figure 
  13 
  is 
  a 
  sketch 
  of 
  the 
  relation 
  here. 
  

  

  It 
  is 
  not 
  certain 
  whether 
  the 
  shale 
  here 
  was 
  originally 
  a 
  wedge 
  

   within 
  the 
  trap, 
  or 
  whether 
  it 
  formed 
  the 
  lower 
  part 
  of 
  the 
  shale 
  

   cover 
  of 
  the 
  trap 
  on 
  this 
  side, 
  into 
  which 
  a 
  thin 
  sheet 
  of 
  the 
  lava 
  

   was 
  extruded, 
  or 
  whether 
  it 
  is 
  due 
  simply 
  to 
  dislocation. 
  

  

  The 
  shear 
  zones. 
  In 
  the 
  nearly 
  vertical 
  shale 
  wedge 
  shown 
  at 
  

   the 
  right 
  in 
  figure 
  12, 
  the 
  shaly 
  material 
  is 
  greatly 
  sheared 
  and 
  

  

  Shale 
  

  

  Trap 
  

  

  Fig. 
  13 
  Sketch 
  of 
  relations 
  of 
  shale 
  and 
  lava 
  on 
  point 
  at 
  the 
  north 
  end 
  of 
  

   the 
  plug, 
  showing 
  a 
  shale 
  wedge 
  with 
  lava 
  above 
  and 
  below 
  

  

  slickensided, 
  as 
  are 
  also 
  the 
  trap 
  surfaces 
  adjoining 
  the 
  shale. 
  

   The 
  grooves 
  and 
  scratches 
  on 
  the 
  slickensided 
  surfaces 
  are 
  nearly 
  

   horizontal 
  in 
  attitude, 
  showing 
  that 
  these 
  two 
  parts 
  of 
  the 
  knob 
  

   have 
  undergone 
  lateral 
  dislocation 
  along 
  a 
  northwest-southeast 
  line. 
  

   Within 
  the 
  northern 
  half 
  of 
  the 
  knob 
  excavation 
  has 
  brought 
  

   to 
  light 
  another 
  great 
  shear 
  zone, 
  nearly 
  vertical 
  and 
  bearing 
  

   north-south. 
  There 
  is 
  no 
  shale 
  wedge 
  here 
  along 
  which 
  displace- 
  

   ment 
  has 
  taken 
  place, 
  but 
  merely 
  a 
  shearing 
  past 
  each 
  other 
  of 
  

   the 
  two 
  adjacent 
  parts 
  of 
  the 
  knob, 
  with 
  production 
  of 
  a 
  highly 
  

   polished 
  and 
  striated 
  contact 
  surface. 
  As 
  in 
  the 
  previous 
  instance, 
  

   the 
  striae 
  are 
  nearly 
  horizontal, 
  in 
  no 
  observed 
  instance 
  departing 
  

   more 
  than 
  20 
  from 
  it. 
  Here 
  again 
  there 
  has 
  been 
  lateral 
  dis- 
  

   placement 
  under 
  conditions 
  of 
  load; 
  in 
  other 
  words, 
  it 
  is 
  incon- 
  

   ceivable 
  that 
  these 
  surfaces 
  of 
  hard 
  trap 
  rock 
  could 
  have 
  been 
  so 
  

   thoroughly 
  smoothed 
  and 
  polished 
  when 
  undergoing 
  lateral 
  slip 
  

  

  