﻿94 
  J. 
  I). 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  

  

  trap 
  filled. 
  It 
  is 
  plain 
  that 
  this 
  chamber 
  could 
  not 
  have 
  been 
  

   so 
  opened 
  in 
  advance 
  of 
  the 
  inflow 
  ; 
  for 
  the 
  hanging 
  wall 
  of 
  

   the 
  weak 
  sandstone 
  inclined 
  65° 
  would 
  have 
  had 
  no 
  support. 
  

   It 
  is 
  hence 
  evident 
  that 
  the 
  ascending 
  stream 
  of 
  trap, 
  forced 
  

  

  Ideal 
  Section 
  of 
  East 
  Rock 
  before 
  the 
  removal 
  of 
  the 
  sandstone 
  from 
  the 
  summit. 
  

  

  along 
  its 
  course, 
  opened 
  a 
  way 
  between 
  the 
  layers; 
  that 
  a 
  

   tongue 
  of 
  trap 
  first 
  entered, 
  which 
  would 
  have 
  been 
  partly 
  

   cooled 
  against 
  the 
  cold 
  rock 
  ; 
  but 
  the 
  flow 
  was 
  kept 
  up 
  below 
  

   this 
  first 
  intruding 
  portion 
  until 
  the 
  trap 
  had 
  all 
  entered, 
  the 
  

   lifting 
  of 
  the 
  overlying 
  sandstone 
  going 
  on 
  as 
  it 
  needed 
  more 
  

   space. 
  This 
  lifting 
  would 
  have 
  brought 
  a 
  strain 
  on 
  the 
  sand- 
  

   stone 
  that 
  would 
  have 
  broken 
  the 
  connection 
  between 
  the 
  

   lifted 
  portion 
  and 
  that 
  either 
  side, 
  to 
  the 
  northward, 
  westward 
  

   and 
  southwestward. 
  To 
  the 
  question, 
  therefore, 
  how 
  far 
  did 
  

   the 
  trap 
  flow 
  westward, 
  the 
  conditions 
  reply 
  : 
  to 
  the 
  wall 
  of 
  

   such 
  a 
  fracture 
  ; 
  and 
  it 
  may 
  not 
  have 
  extended 
  many 
  rods 
  

   beyond 
  the 
  present 
  limit. 
  The 
  sandstone 
  of 
  the 
  western 
  wall 
  

   has 
  disappeared 
  in 
  the 
  general 
  denudation 
  over 
  the 
  ISTew 
  

   Haven 
  region, 
  excepting 
  a 
  small 
  part 
  at 
  the 
  southwest 
  angle, 
  

   where 
  a 
  zigzag 
  path 
  (Z, 
  Plate 
  III) 
  ascends 
  to 
  its 
  top 
  ; 
  the 
  

   height 
  of 
  this 
  sandstone 
  is 
  185 
  feet, 
  which 
  is 
  twenty-five 
  feet 
  

   above 
  the 
  base 
  of 
  the 
  trap 
  where 
  highest 
  to 
  the 
  northward, 
  

   and 
  fifty 
  feet 
  . 
  above 
  that 
  just 
  south 
  at 
  A'. 
  The 
  locality 
  of 
  

   this 
  sandstone 
  and 
  the 
  zigzag 
  path 
  is 
  seen 
  on 
  the 
  right 
  margin 
  

   of 
  Plate 
  IV. 
  The 
  sandstone 
  of 
  the 
  northern 
  wall 
  remains 
  

   to 
  a 
  height 
  of 
  196 
  feet 
  at 
  m 
  : 
  the 
  sandstone 
  between 
  Whitney 
  

   Peak 
  and 
  East 
  Pock 
  is 
  what 
  is 
  left 
  of 
  it. 
  The 
  dip 
  of 
  this 
  

   sandstone 
  at 
  m, 
  near 
  the 
  junction, 
  is 
  30°, 
  in 
  the 
  direction 
  ]S". 
  

   73° 
  E. 
  ; 
  and 
  the 
  inclination 
  of 
  the 
  columns 
  of 
  the 
  trap 
  just 
  

   above 
  is 
  also 
  30°. 
  

  

  The 
  theoretical 
  section 
  of 
  East 
  Pock 
  in 
  fig. 
  10 
  represents 
  

   correctly 
  the 
  fact 
  of 
  the 
  intrusion 
  of 
  the 
  melted 
  trap 
  between 
  

   sandstone 
  layers. 
  But 
  since 
  the 
  bottom 
  over 
  which 
  the 
  flow 
  

   took 
  place 
  is 
  concealed 
  from 
  view, 
  it 
  is 
  not 
  quite 
  certain 
  that 
  

   the 
  sandstone 
  layer 
  on 
  which 
  the 
  flow 
  began 
  continued 
  to 
  

   be 
  the 
  floor 
  to 
  its 
  western 
  limit. 
  Moreover, 
  there 
  is 
  a 
  large 
  

   discrepancy 
  between 
  the 
  pitch 
  of 
  the 
  trap 
  over 
  the 
  summit 
  

   and 
  that 
  in 
  the 
  section. 
  An 
  actual 
  section 
  of 
  the 
  rock 
  from 
  

  

  