﻿J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  83 
  

  

  spaces 
  or 
  chambers 
  for 
  its 
  occupation, 
  the 
  liquid 
  rock 
  thus 
  

   lifting 
  the 
  overlying 
  sandstone 
  as 
  long 
  as 
  the 
  discharge 
  was 
  

   continued. 
  By 
  such 
  means 
  the 
  sheets 
  of 
  liquid 
  trap 
  attained, 
  

   in 
  some 
  cases, 
  a 
  thickness 
  of 
  300 
  or 
  more 
  feet. 
  This 
  forcible 
  

   opening 
  and 
  filling 
  of 
  a 
  chamber 
  in 
  the 
  sandstone 
  by 
  the 
  up- 
  

   thrust 
  lavas, 
  is 
  a 
  laccolithic 
  process, 
  it 
  according 
  with 
  that 
  of 
  the 
  

   typical 
  laccoliths 
  ably 
  studied 
  out 
  and 
  described 
  by 
  Gilbert.* 
  

  

  (5). 
  The 
  intrusion 
  of 
  the 
  flowing 
  rock 
  between 
  the 
  sandstone 
  

   layers 
  took 
  place 
  at 
  comparatively 
  shallow 
  depths, 
  where 
  the 
  

   pressure 
  of 
  the 
  rock 
  was 
  not 
  too 
  great 
  to 
  prevent 
  it. 
  

  

  (6). 
  It 
  was 
  favored, 
  in 
  each 
  case, 
  by 
  the 
  fact 
  that 
  the 
  

   oblique 
  fissure 
  supplying 
  the 
  lava 
  was 
  inclined 
  in 
  the 
  same 
  

   direction 
  with 
  the 
  layers 
  of 
  the 
  uplifted 
  sandstone 
  — 
  both 
  in- 
  

   clining 
  westward, 
  the 
  dip 
  being 
  eastward. 
  

  

  (7). 
  The 
  termination 
  of 
  a 
  fissure 
  in 
  several 
  outlets, 
  exempli- 
  

   fied 
  in 
  three 
  of 
  the 
  Rocks, 
  was 
  largely 
  due 
  to 
  the 
  great 
  incli- 
  

   nation 
  and 
  depth 
  of 
  the 
  fissures 
  opened 
  through 
  the 
  weak 
  

   upturned 
  and 
  faulted 
  sandstone, 
  and 
  thence 
  to 
  great 
  downfalls 
  

   of 
  the 
  hanging 
  wall. 
  The 
  same 
  cause 
  led 
  to 
  irregularities 
  in 
  

   the 
  width 
  and 
  forms 
  of 
  dikes, 
  and 
  influenced 
  the 
  outlines 
  and 
  

   surface-features 
  of 
  outflows. 
  

  

  (8). 
  The 
  course 
  and 
  dip 
  of 
  supply-fissures 
  was 
  not 
  deter- 
  

   mined 
  by 
  the 
  foliation 
  or 
  bedding 
  of 
  the 
  schists 
  underneath 
  

   the 
  sandstone. 
  

  

  2. 
  Special 
  facts 
  from 
  the 
  several 
  Hocks 
  illustrating 
  the 
  

   above 
  conclusions. 
  

  

  The 
  ridges, 
  Fine 
  Rock 
  and 
  Mill 
  Hock, 
  containing 
  simple 
  

   dikes 
  are 
  first 
  considered, 
  and 
  then 
  East 
  Rock 
  and 
  West 
  Rock, 
  

   which 
  include 
  dikes 
  and 
  outflows 
  from 
  them.f 
  

  

  1. 
  PINE 
  ROCK. 
  

  

  The 
  general 
  form 
  of 
  Pine 
  Rock 
  is 
  shown 
  on 
  Plate 
  II, 
  and 
  

   still 
  better 
  on 
  the 
  following 
  larger 
  map. 
  J 
  It 
  is 
  only 
  three- 
  

   fourths 
  of 
  a 
  mile 
  long 
  and 
  trends 
  X. 
  67° 
  E., 
  or 
  east-northeast. 
  

   This 
  small 
  ridge 
  has 
  three, 
  perhaps 
  four, 
  independent 
  outlets 
  

   of 
  trap, 
  A, 
  BB', 
  CC 
  / 
  and 
  D. 
  The 
  first, 
  at 
  the 
  west 
  end, 
  is 
  a 
  

   small 
  dike 
  15 
  to 
  20 
  feet 
  wide, 
  trending 
  north 
  20° 
  west, 
  and 
  

   traceable 
  for 
  220 
  feet. 
  It 
  dips 
  eastward 
  25°, 
  and 
  thus 
  proves 
  

  

  * 
  Geology 
  of 
  the 
  Henry 
  Mountains 
  by 
  G. 
  K. 
  Gilbert. 
  4to, 
  1877. 
  

  

  f 
  In 
  justice 
  to 
  Percival, 
  the 
  author 
  of 
  the 
  Report 
  on 
  the 
  Geology 
  of 
  Connecti- 
  

   cut 
  of 
  1842, 
  it 
  should 
  be 
  here 
  stated 
  that 
  there 
  is 
  scarcely 
  an 
  outlet 
  or 
  area 
  of 
  

   trap 
  mentioned 
  beyond 
  which 
  is 
  not 
  recorded 
  on 
  his 
  map 
  or 
  described 
  in 
  his 
  

   Report. 
  

  

  X 
  The 
  contour 
  lines 
  on 
  this 
  map, 
  and 
  also 
  those 
  on 
  that 
  of 
  Mill 
  Rock 
  on 
  page 
  

   ■87, 
  are 
  copied 
  from 
  the 
  Bache 
  Coast 
  Survey 
  map. 
  

  

  