﻿J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non-volcanic 
  Igneous 
  Ejections. 
  81 
  

  

  and 
  coarse 
  conglomerate, 
  even 
  cobble-stone-gravel 
  conglomer- 
  

   ate. 
  When 
  line-grained 
  and 
  shaly 
  it 
  is 
  not 
  a 
  firm 
  laminated 
  

   rock, 
  bnt 
  divides 
  or 
  crumbles 
  readily 
  to 
  thin 
  chips. 
  The 
  more 
  

   massive 
  kinds 
  are 
  usually 
  traversed 
  with 
  fractures 
  ; 
  and 
  none 
  

   has 
  much 
  firmness 
  except 
  where 
  consolidated 
  by 
  heat 
  from 
  the 
  

   trap-ejections, 
  or 
  the 
  hot 
  vapors 
  produced 
  thereby. 
  Conse- 
  

   quently, 
  fissures 
  made 
  though 
  the 
  formation 
  should 
  have 
  great 
  

   irregularities, 
  from 
  irregular 
  fracturing 
  and 
  the 
  tumbling 
  into 
  

   them 
  of 
  masses 
  of 
  sandstone 
  and 
  large 
  sections 
  of 
  their 
  walls. 
  

  

  (2) 
  The 
  thickness 
  of 
  the 
  sandstone 
  intersected 
  by 
  the 
  fissures 
  

   over 
  the 
  center 
  of 
  the 
  Xew 
  Haven 
  region 
  was 
  at 
  least 
  3000 
  

   feet, 
  as 
  proved 
  by 
  borings 
  at 
  a 
  point 
  half 
  way 
  between 
  the 
  bay 
  

   and 
  the 
  west 
  end 
  of 
  Mill 
  Rock. 
  Along 
  the 
  West 
  Eock 
  line 
  

   the 
  depth 
  was 
  probably 
  less, 
  as 
  this 
  ridge 
  is 
  within 
  a 
  mile 
  

   and 
  a 
  half 
  of 
  the 
  western 
  metamorphic 
  limit 
  of 
  the 
  Connecti- 
  

   cut 
  Valley 
  of 
  Triassic 
  time. 
  Beneath 
  the 
  sandstone 
  the 
  fissures 
  

   came 
  up 
  through 
  underlying 
  crystalline 
  rocks, 
  in 
  which 
  they 
  

   would 
  probably 
  have 
  great 
  regularity 
  in 
  course, 
  width 
  and 
  con- 
  

   tinuity. 
  

  

  (3) 
  When 
  the 
  heat 
  from 
  the 
  trap, 
  or 
  the 
  hot 
  vapors 
  gener- 
  

   ated 
  by 
  it, 
  consolidated 
  the 
  sandstone, 
  it 
  generally 
  made 
  hard, 
  

   durable 
  rock 
  of 
  the 
  coarser 
  kind, 
  but 
  left 
  the 
  finer 
  beds, 
  

   alternating 
  with 
  the 
  coarse, 
  fragile 
  and 
  chip-making 
  ; 
  and 
  this 
  

   was 
  so, 
  apparently, 
  because 
  hot 
  vapor 
  penetrates 
  most 
  easily 
  

   the 
  coarser 
  beds 
  for 
  the 
  cementing 
  work. 
  The 
  heat 
  through 
  

   the 
  penetrating 
  vapors, 
  generally 
  discharged 
  more 
  or 
  less 
  com- 
  

   pletely 
  the 
  color 
  of 
  the 
  beds 
  it 
  consolidated, 
  producing 
  an 
  ash- 
  

   gray 
  and 
  brownish 
  shade 
  ; 
  made 
  in 
  them 
  steam 
  tubes 
  with 
  

   blanched 
  walls 
  ; 
  produced 
  blotches 
  of 
  impure 
  chlorite, 
  or 
  

   epidote, 
  and 
  crystallizations 
  of 
  hematite 
  and 
  epidote, 
  and 
  less 
  

   commonly 
  garnet. 
  But 
  the 
  finer 
  beds 
  that 
  alternate 
  with 
  the 
  

   coarse 
  commonly 
  retain, 
  except 
  perhaps 
  for 
  a 
  few 
  inches, 
  their 
  

   red 
  color, 
  and 
  even 
  have 
  it 
  deepened 
  to 
  a 
  dark 
  purplish 
  red 
  — 
  

   as 
  if 
  by 
  the 
  reduction 
  of 
  some 
  of 
  the 
  red 
  coloring 
  matter 
  

   (oxide 
  of 
  iron) 
  to 
  magnetite. 
  Moreover, 
  the 
  sandstone 
  often 
  

   loses 
  all 
  the 
  old 
  bedding. 
  These 
  varying 
  effects 
  from 
  the 
  heat 
  

   have 
  added 
  much 
  to 
  the 
  original 
  irregularities 
  of 
  the 
  beds. 
  

  

  (1) 
  Of 
  the 
  four 
  Rocks, 
  East 
  and 
  West 
  belong 
  to 
  the 
  prevail- 
  

   ing 
  north-and- 
  south 
  system, 
  as 
  already 
  stated; 
  the 
  other 
  two, 
  

   Pine 
  Rock 
  and 
  Mill 
  Rock, 
  to 
  a 
  transverse 
  system. 
  

  

  (2) 
  In 
  East 
  Rock 
  and 
  West 
  Rock 
  the 
  sheet 
  of 
  trap 
  made 
  

   by 
  outfiow 
  from 
  the 
  opened 
  fissure 
  or 
  fissures 
  has 
  a 
  length 
  

   westward 
  of 
  100 
  to 
  500 
  yards. 
  

  

  (3) 
  The 
  supply 
  fissure, 
  or 
  its 
  filling, 
  the 
  dike, 
  descends 
  be- 
  

   neath 
  the 
  eastern 
  slope 
  with 
  a 
  large 
  eastward 
  pitch 
  : 
  the 
  angle 
  

   of 
  pitch 
  in 
  the 
  case 
  of 
  East 
  Rock 
  being 
  about 
  50°. 
  

  

  