﻿GEOLOGY 
  OF 
  SARATOGA 
  SPRINGS 
  AND 
  VICINITY 
  II7 
  

  

  this 
  fault, 
  but 
  the 
  figure 
  is 
  purposely 
  drawn 
  with 
  some 
  vagueness 
  on 
  the 
  

   extreme 
  left 
  of 
  the 
  igneous 
  rock. 
  

  

  To 
  sum 
  up 
  the 
  geologic 
  relations 
  of 
  the 
  Stark's 
  knob 
  igneous 
  mass, 
  it 
  is 
  

   surrounded 
  on 
  all 
  sides 
  by 
  the 
  Hudson 
  river 
  slates. 
  The 
  principal 
  mass 
  is 
  

   relatively 
  faulted 
  down 
  into 
  these 
  sedimentary 
  rocks 
  on 
  the 
  south 
  and 
  east. 
  

   To 
  the 
  eye 
  there 
  appears 
  no 
  distinct 
  evidence 
  of 
  contact 
  metamorphism; 
  yet 
  

   the 
  mass 
  appears 
  to 
  be 
  the 
  superficial 
  portion 
  of 
  a 
  body 
  which 
  extends 
  

   downward 
  into 
  the 
  slates 
  and, 
  from 
  its 
  general 
  form 
  and 
  surroundings, 
  

   strongly 
  suggests 
  a 
  neck 
  or 
  plug 
  rising 
  up 
  through 
  the 
  Hudson 
  river 
  group 
  

   at 
  this 
  point. 
  The 
  manner 
  in 
  which 
  the 
  slate 
  body 
  dips 
  beneath 
  the 
  igneous 
  

   mass 
  on 
  the 
  northeast, 
  expressed 
  in 
  figure 
  9, 
  appears 
  to 
  indicate 
  that 
  the 
  

   neck 
  or 
  plug 
  does 
  not 
  extend 
  vertically 
  downward 
  through 
  the 
  slates 
  but 
  

   follows 
  guiding 
  planes 
  of 
  structure. 
  It 
  is 
  conceivable 
  that 
  the 
  igneous 
  rock 
  

   once 
  overlay 
  the 
  surface 
  of 
  the 
  slates, 
  has 
  been 
  tilted 
  with 
  them 
  in 
  one 
  

   of 
  the 
  orogenic 
  movements 
  of 
  the 
  region, 
  and 
  has 
  subsequently 
  been 
  faulted 
  

  

  Fig. 
  9 
  Cross 
  section 
  .of 
  Stark's 
  knob, 
  showing 
  general 
  relation 
  

   to 
  the 
  slates, 
  and 
  the 
  gross 
  ball 
  structure 
  of 
  the 
  mass 
  

  

  and 
  thus 
  separated 
  from 
  other 
  masses 
  of 
  igneous 
  rock 
  which 
  are 
  now 
  

   removed 
  by 
  erosion; 
  but 
  this 
  view 
  is 
  not 
  borne 
  out 
  by 
  the 
  observed 
  geologic 
  

   relations 
  as 
  now 
  exposed. 
  

  

  Structure 
  of 
  the 
  Stark's 
  knob 
  rock. 
  The 
  rock 
  of 
  which 
  Stark's 
  knob 
  

   is 
  composed 
  is 
  complex 
  in 
  structure. 
  The 
  exposed 
  faces 
  exhibit 
  cross 
  sections 
  

   of 
  ball 
  and 
  pear-shaped 
  masses 
  embedded 
  in 
  a 
  base 
  having 
  a 
  shaly 
  structure. 
  

   The 
  crust 
  of 
  these 
  balls 
  consists 
  of 
  a 
  layer 
  of 
  a 
  dense, 
  dark 
  colored 
  basic 
  

   rock 
  of 
  the 
  diabase 
  type, 
  surrounding 
  a 
  variable 
  nucleus 
  of 
  ashy, 
  rather 
  

   porous, 
  pumiceous-looking 
  lava 
  in 
  most 
  cases, 
  and 
  more 
  rarely 
  an 
  included 
  

   marginally 
  absorbed 
  fragment 
  of 
  white, 
  semicrystalline 
  limestone. 
  

  

  The 
  line 
  of 
  demarcation 
  between 
  these 
  three 
  elements 
  in 
  the 
  rock 
  structure 
  

   is 
  usually 
  very 
  sharp 
  and, 
  where 
  the 
  shaly, 
  fine 
  grained 
  base 
  has 
  peeled 
  away 
  

   from 
  the 
  surface 
  of 
  the 
  lava 
  balls, 
  the 
  surface 
  of 
  the 
  latter 
  resembles 
  the 
  

   coarse, 
  bulging 
  flowage 
  surface 
  of 
  basalt 
  streams, 
  such 
  as 
  are 
  seen 
  in 
  Hawaii. 
  

   The 
  whole 
  has 
  the 
  appearance 
  of 
  a 
  mass 
  of 
  bombs 
  or 
  lava 
  balls 
  inclosing 
  

   scoriaceous 
  lava, 
  or 
  foreign 
  inclusions 
  embedded 
  in 
  a 
  basaltic 
  glass 
  which 
  

   has 
  devitrified 
  and 
  is 
  scaling 
  to 
  pieces 
  along 
  lines 
  of 
  flowage. 
  A 
  more 
  

   probable 
  explanation 
  of 
  the 
  structure 
  is 
  that 
  this 
  mass 
  represents 
  a 
  volcanic 
  

   throat 
  or 
  plug 
  at 
  some 
  depth 
  below 
  the 
  actual 
  vent 
  or 
  crater 
  but 
  not 
  below 
  the 
  

   point 
  to 
  which 
  explosive 
  products 
  may 
  have 
  fallen 
  back 
  in 
  the 
  volcano 
  there 
  

   to 
  become 
  embedded 
  in 
  still 
  hot 
  lava. 
  Certainly 
  the 
  gross 
  structure 
  of 
  the 
  

   rock 
  recalls 
  many 
  lava 
  sheets 
  with 
  locally 
  formed 
  explosive 
  products, 
  and 
  

   the 
  same 
  structure 
  is 
  to 
  be 
  observed 
  in 
  the 
  lava 
  flows 
  of 
  the 
  Newark 
  formation 
  

  

  