﻿96 
  J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  

  

  would 
  probably 
  represent 
  the 
  position 
  of 
  the 
  bottom 
  of 
  the 
  

   outflow. 
  The 
  line 
  d 
  I" 
  V 
  I 
  has 
  been 
  drawn 
  on 
  this 
  view. 
  It 
  

   supposes 
  that 
  the 
  trap, 
  on 
  leaving 
  the.dike, 
  passed 
  between 
  two 
  

   layers 
  of 
  sandstone 
  from 
  I 
  to 
  U 
  and 
  that 
  afterward 
  it 
  broke 
  

   away 
  the 
  layer 
  beneath 
  it 
  and 
  flowed 
  on, 
  either 
  over 
  the 
  edges 
  

   or 
  surfaces 
  of 
  layers 
  as 
  the 
  conditions 
  favored. 
  

  

  The 
  only 
  spot 
  where 
  a 
  section 
  of 
  the 
  floor 
  or 
  plane 
  of 
  junc- 
  

   tion 
  of 
  trap 
  and 
  sandstone, 
  is 
  seen, 
  is 
  at 
  A', 
  the 
  south-south- 
  

   west 
  corner 
  of 
  the 
  trap-mass, 
  by 
  the 
  road-side. 
  There, 
  for 
  a 
  few 
  

   yards, 
  the 
  trap 
  rests 
  on 
  upturned 
  ledges 
  of 
  sandstone, 
  and 
  not 
  

   on 
  one 
  continuous 
  layer. 
  The 
  section 
  is 
  too 
  short 
  for 
  any 
  reli- 
  

   able 
  conclusion 
  were 
  it 
  not 
  sustained 
  by 
  facts 
  from 
  West 
  Rock. 
  

  

  The 
  section, 
  fig. 
  11, 
  also 
  represents 
  the 
  inner 
  and 
  outer 
  

   dikes 
  described 
  above, 
  with 
  the 
  intervening 
  (?) 
  sandstone. 
  The 
  

   doubts 
  with 
  regard 
  to 
  the 
  widths 
  of 
  these 
  dikes 
  and 
  the 
  area 
  

   of 
  sandstone 
  have 
  already 
  been 
  the 
  subject 
  of 
  remark. 
  

  

  Columns 
  stand 
  out 
  boldly 
  on 
  the 
  steep 
  western 
  front 
  of 
  East 
  

   Rock. 
  But 
  they 
  have 
  none 
  of 
  the 
  normal 
  forms, 
  for 
  the 
  angle 
  

   between 
  the 
  most 
  prominent 
  faces 
  frequently 
  approaches 
  a 
  

   right 
  angle, 
  resulting 
  from 
  a 
  combination 
  of 
  the 
  plane 
  of 
  frac- 
  

   ture 
  at 
  right 
  angles 
  to 
  the 
  trap-mass 
  and 
  another 
  transverse. 
  

   The 
  direction 
  of 
  these 
  planes 
  varies 
  along 
  the 
  course 
  of 
  the 
  

   Rock 
  on 
  account 
  of 
  the 
  curve 
  in 
  its 
  outlines. 
  At 
  the 
  quarry, 
  

   on 
  the 
  south 
  side 
  of 
  the 
  summit, 
  at 
  the 
  termination 
  of 
  the 
  

   zigzag 
  path 
  Z, 
  there 
  is 
  a 
  fine 
  display 
  of 
  broad 
  surfaces 
  in 
  the 
  

   two 
  directions 
  meeting 
  nearly 
  at 
  a 
  right 
  angle. 
  The 
  courses 
  

   here 
  are 
  about 
  N. 
  35° 
  E. 
  and 
  K 
  55° 
  W. 
  The 
  surface 
  of 
  one 
  

   of 
  them 
  for 
  many 
  square 
  yards 
  is 
  covered 
  with 
  rosettes 
  of 
  

   garnets 
  and 
  scattered 
  minute 
  crystals 
  of 
  magnetite, 
  their 
  faces 
  

   brilliant 
  in 
  the 
  sunshine. 
  Along 
  the 
  whole 
  western 
  front 
  

   of 
  the 
  Rock 
  there 
  is 
  a 
  remarkable 
  predominance 
  of 
  planes 
  

   conforming 
  to 
  its 
  plane 
  through 
  all 
  its 
  changes 
  of 
  direction. 
  

   This 
  is 
  apparent 
  on 
  Plate 
  IV, 
  and 
  some 
  of 
  the 
  right 
  angles 
  

   are 
  seen 
  on 
  Plate 
  V. 
  

  

  The 
  upper 
  half 
  of 
  the 
  columnar 
  front 
  (see 
  Plate 
  IY), 
  down 
  

   to 
  a 
  level 
  of 
  about 
  220 
  feet 
  above 
  tide-level, 
  has 
  columns 
  

   four 
  to 
  eight 
  feet 
  in 
  diameter 
  ; 
  below 
  this 
  the 
  size 
  is 
  in 
  general 
  

   half 
  less 
  ; 
  and 
  for 
  the 
  lower 
  twenty 
  feet 
  above 
  the 
  sandstone, 
  

   they 
  are 
  quite 
  small. 
  

  

  Indian 
  Head. 
  — 
  Indian 
  Head 
  is 
  much 
  like 
  a 
  small 
  edition 
  

   of 
  East 
  Rock. 
  The 
  length 
  of 
  the 
  outflow 
  is 
  100 
  yards 
  ; 
  the 
  

   height 
  310 
  feet 
  (313 
  above 
  mean 
  tide). 
  A 
  section 
  made 
  on 
  

   the 
  same 
  principle 
  with 
  fig. 
  11 
  of 
  East 
  Rock 
  is 
  given 
  in 
  fig. 
  12. 
  

  

  Indian 
  Head 
  stands 
  quite 
  apart 
  from 
  East 
  Rock. 
  The 
  

   gap 
  now 
  separating 
  them, 
  where 
  highest, 
  is 
  about 
  200 
  feet 
  

   above 
  high 
  tide, 
  and 
  therefore 
  nearly 
  160 
  feet 
  below 
  the 
  top 
  

  

  