﻿J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  107 
  

  

  460, 
  but 
  also 
  440 
  on 
  the 
  north 
  side 
  is 
  to 
  the 
  west 
  of 
  440 
  of 
  the 
  

   south 
  side 
  ; 
  but 
  the 
  height 
  of 
  440 
  to 
  the 
  north 
  is 
  probably 
  pro- 
  

   duced 
  with 
  a 
  less 
  thickness 
  of 
  trap. 
  This 
  notch 
  is 
  300 
  yards 
  

   south 
  of 
  the 
  Buttress 
  dike 
  described 
  on 
  a 
  former 
  page 
  ; 
  the 
  

   position 
  of 
  this 
  dike 
  is 
  shown 
  on 
  the 
  above 
  figure 
  at 
  b. 
  

  

  This 
  example 
  will 
  suffice 
  for 
  illustration. 
  Other 
  gaps 
  in 
  the 
  

   ridge 
  occur 
  farther 
  north, 
  but 
  they 
  are 
  outside 
  of 
  the 
  region 
  

   here 
  under 
  consideration. 
  

  

  Obstructions 
  to 
  the 
  outflow 
  of 
  lava 
  while 
  it 
  was 
  making 
  its 
  

   way 
  between 
  the 
  layers 
  of 
  sandstone 
  are 
  also 
  possible 
  through 
  

   any 
  cause 
  that 
  would 
  prevent 
  the 
  lifting 
  of 
  any 
  portion 
  of 
  the 
  

   overlying 
  rock. 
  The 
  area 
  of 
  the 
  Triangle 
  has 
  been 
  described 
  

   as 
  an 
  area 
  of 
  sandstone 
  within 
  the 
  proper 
  limits 
  of 
  the 
  trap 
  

   range. 
  This 
  sandstone 
  was 
  not 
  lifted 
  like 
  the 
  rest 
  of 
  the 
  over- 
  

   lying 
  stratum. 
  Instead 
  of 
  this, 
  it 
  remained 
  in 
  place 
  for 
  the 
  

   most 
  part, 
  and 
  hence, 
  forced 
  the 
  liquid 
  rock 
  to 
  pass 
  to 
  one 
  side 
  

   of 
  it. 
  The 
  lava, 
  mainly 
  took 
  the 
  north 
  side 
  ; 
  and 
  so 
  the 
  trap 
  

   of 
  that 
  side 
  had 
  its 
  surface 
  raised 
  in 
  level 
  above 
  the 
  rock 
  

   north 
  and 
  became 
  the 
  elevated 
  embossed 
  area 
  already 
  described. 
  

   The 
  great 
  sloping 
  trap 
  wall 
  making 
  the 
  north 
  side 
  of 
  the 
  

   Triangle 
  is 
  the 
  wall 
  of 
  an 
  oblique 
  fissure 
  in 
  the 
  sandstone 
  for- 
  

   mation. 
  Along 
  this 
  fissure 
  — 
  45° 
  in 
  inclination,— 
  the 
  sandstone 
  

   of 
  the 
  south 
  side, 
  or 
  that 
  of 
  the 
  Triangle, 
  lay 
  unmoved 
  or 
  

   nearly 
  so. 
  while 
  that 
  of 
  the 
  north 
  side 
  was 
  shoved 
  up 
  as 
  the 
  

   lavas 
  came 
  in 
  below. 
  Other 
  walls, 
  and 
  the 
  small 
  ridges 
  both 
  

   north 
  and 
  south 
  of 
  the 
  Triangle, 
  are 
  evidences 
  of 
  similar 
  frac- 
  

   tures, 
  in 
  parallel 
  directions, 
  with 
  analogous 
  results. 
  The 
  

   unlifted 
  sandstone 
  was 
  in 
  some 
  way 
  put 
  under 
  a 
  strain 
  that 
  

   produced 
  the 
  parallel 
  fracturing 
  and 
  movements. 
  

  

  The 
  origin 
  of 
  the 
  southern 
  or 
  western 
  walls 
  of 
  West 
  Eock 
  

   is 
  sufficiently 
  explained 
  in 
  the 
  remarks 
  on 
  this 
  subject 
  respect- 
  

   ing 
  East 
  Eock 
  (page 
  94). 
  

  

  The 
  southern 
  front 
  of 
  West 
  Eock 
  has 
  a 
  columnar 
  aspect. 
  

   But 
  in 
  reality 
  no 
  columns 
  stand 
  out 
  with 
  the 
  boldness 
  they 
  

   have 
  in 
  East 
  Eock. 
  The 
  surface 
  is 
  mostly 
  made 
  up 
  of 
  the 
  

   cleavage 
  surface 
  or 
  joints 
  that 
  are 
  in 
  its 
  plane 
  ; 
  and 
  where 
  

   there 
  has 
  been 
  quarrying, 
  these 
  joints 
  have 
  great 
  width 
  as 
  

   well 
  as 
  height. 
  

  

  3. 
  Relation 
  of 
  the 
  east-axd-west 
  axd 
  xorth-axd-south 
  

   fissures, 
  axd 
  the 
  origix 
  of 
  these 
  courses. 
  

  

  These 
  two 
  courses 
  of 
  fissures 
  are 
  so 
  locked 
  together 
  in 
  the 
  

   Xew 
  Haven 
  region 
  that 
  they 
  evidently 
  are 
  results 
  of 
  one 
  sys- 
  

   tem 
  of 
  movements. 
  They 
  occur 
  together 
  in 
  Pine 
  Eock 
  ; 
  and 
  

   West 
  Rock 
  has 
  the 
  general 
  trend 
  of 
  the 
  Pine 
  Eock 
  ridge 
  

   represented 
  in 
  the 
  embossed 
  area 
  and 
  the 
  southeast 
  point. 
  

  

  