﻿J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  87 
  

  

  the 
  western, 
  AA', 
  the 
  eastern, 
  BE' 
  ; 
  north 
  of 
  the 
  gap 
  between 
  

   these, 
  a 
  short 
  narrow 
  dike 
  C, 
  and 
  farther 
  north, 
  the 
  isolated 
  

   area, 
  D. 
  The 
  width 
  of 
  the 
  first, 
  AA', 
  (as 
  measured 
  at 
  its 
  west 
  

   end) 
  is 
  200 
  feet 
  ; 
  of 
  the 
  second, 
  140 
  or 
  150 
  feet 
  ; 
  of 
  the 
  third, 
  

   1 
  to 
  10 
  feet 
  ; 
  of 
  the 
  fourth, 
  50 
  feet, 
  the 
  length 
  being 
  150. 
  

   The 
  mass 
  BB' 
  continues 
  to 
  Mill 
  River 
  where 
  the 
  surface 
  of 
  the 
  

   country 
  declines 
  to 
  tide 
  level. 
  But 
  the 
  trap 
  does 
  not 
  stop 
  

   here 
  ; 
  it 
  crosses 
  the 
  river 
  and 
  extends 
  on 
  eastward, 
  with 
  an 
  in- 
  

   creased 
  width, 
  180 
  feet, 
  to 
  the 
  summit 
  of 
  Whitney 
  Peak. 
  

   The 
  Whitney 
  Peak 
  dike 
  belongs 
  therefore 
  to 
  the 
  Mill 
  Rock 
  

   region, 
  although 
  topographically 
  part 
  of 
  the 
  East 
  Rock 
  area. 
  

   The 
  trend 
  of 
  the 
  Whitney 
  Peak 
  portion 
  is 
  S. 
  68° 
  E.; 
  of 
  AA', 
  

   S. 
  78° 
  E. 
  The 
  mean 
  course 
  for 
  the 
  whole 
  series 
  to 
  the 
  summit 
  

   of 
  Whitney 
  Peak 
  is 
  about 
  S. 
  72° 
  E. 
  

  

  Map 
  of 
  Mill 
  Rock, 
  excepting 
  its 
  eastern 
  extremity. 
  Trap 
  areas 
  with 
  dotted 
  

   outlines. 
  

  

  The 
  dip 
  or 
  pitch 
  of 
  the 
  main 
  dike 
  is 
  about 
  72° 
  to 
  the 
  north- 
  

   ward, 
  or 
  18° 
  from 
  the 
  vertical. 
  This 
  inclination 
  and 
  the 
  course 
  

   of 
  the 
  "columnar 
  fractures 
  are 
  

   well 
  exhibited 
  at 
  the 
  west 
  end 
  

   of 
  the 
  dike, 
  A, 
  and 
  are 
  repre- 
  

   sented 
  in 
  figure 
  b\ 
  

  

  Besides 
  the 
  columnar 
  frac- 
  

   tures 
  at 
  right 
  angles 
  to 
  the 
  

  

  llA 
  i 
  ° 
  -i 
  & 
  i 
  ., 
  j. 
  Section 
  of 
  Mill 
  Rock, 
  west 
  end. 
  

  

  walls, 
  there 
  are 
  also 
  longitudi- 
  

   nal 
  fractures 
  in 
  interrupted 
  lines, 
  parallel 
  to 
  the 
  walls. 
  Two 
  

   are 
  seen 
  at 
  the 
  west 
  end 
  of 
  the 
  Rock 
  and 
  are 
  indicated 
  in 
  the 
  

   above 
  figure. 
  They 
  are 
  now 
  mineral 
  veins. 
  The 
  more 
  south- 
  

  

  