﻿J. 
  D. 
  Dana 
  — 
  Features 
  of 
  non- 
  volcanic 
  Igneous 
  Ejections. 
  105 
  

  

  The 
  trap 
  of 
  this 
  ridge, 
  at 
  a 
  higher 
  level 
  above 
  the 
  sandstone, 
  

   is 
  more 
  or 
  less 
  chloritic 
  and 
  in 
  many 
  places 
  amygdaloidal. 
  

   Part 
  of 
  the 
  amygdules 
  are 
  slender 
  cylinders, 
  two 
  to 
  three 
  

   inches 
  long 
  and 
  like 
  pipe-stems 
  in 
  size, 
  occurring 
  often 
  in 
  

   groups 
  — 
  the 
  result 
  probably 
  of 
  the 
  sudden 
  vaporization 
  of 
  

   particles 
  of 
  liquid 
  carbonic 
  acid. 
  

  

  In 
  the 
  railroad 
  gap 
  through 
  the 
  Saltonstall 
  Ridge, 
  the 
  first 
  

   west 
  of 
  Saltonstall 
  Lake 
  ('• 
  Pond 
  Ridge 
  " 
  of 
  Percival), 
  the 
  

   sandstone 
  appears 
  to 
  lie 
  in 
  a 
  similar 
  manner 
  unconformably 
  

   beneath 
  the 
  western 
  extension 
  of 
  the 
  trap. 
  But 
  the 
  section 
  is 
  

   now 
  too 
  mnch 
  covered 
  by 
  debris 
  for 
  a 
  satisfactory 
  observation. 
  

   Two 
  miles 
  east 
  of 
  the 
  Saltonstall 
  ridge 
  in 
  Branford, 
  as 
  de- 
  

   scribed 
  by 
  Mr. 
  E. 
  O. 
  Hovey,* 
  the 
  trap 
  of 
  a 
  short 
  range, 
  the 
  

   easternmost 
  in 
  this 
  part 
  of 
  the 
  sandstone 
  region 
  and 
  near 
  the 
  

   gneiss 
  boundary, 
  overlies 
  the 
  upturned 
  edges 
  of 
  the 
  sandstone, 
  

   and 
  there 
  is 
  between 
  the 
  two 
  rocks 
  a 
  layer 
  of 
  sandstone 
  con- 
  

   glomerate 
  containing 
  nodules 
  of 
  trap, 
  which 
  he 
  attributed 
  to 
  

   the 
  rubbing 
  action 
  of 
  the 
  flowing 
  trap 
  on 
  the 
  sandstone. 
  

  

  These 
  facts, 
  ranging 
  in 
  this 
  part 
  of 
  the 
  Connecticut 
  Valley 
  

   over 
  the 
  whole 
  breadth 
  of 
  the 
  Jnra-Trias 
  formation, 
  from 
  the 
  

   west 
  side 
  of 
  the 
  New 
  Haven 
  region 
  where 
  the 
  trap 
  is 
  of 
  the 
  

   compact 
  non-vesicular 
  kind 
  to 
  the 
  dikes 
  of 
  vesicular 
  trap 
  

   toward 
  and 
  near 
  the 
  eastern 
  gneissic 
  border, 
  have 
  great 
  impor- 
  

   tance 
  in 
  their 
  bearing 
  on 
  the 
  subject 
  of 
  the 
  other 
  Jura-Trias 
  

   ridges. 
  The 
  more 
  eastern 
  are 
  placed 
  by 
  Professor 
  Davis 
  

   among 
  the 
  ridges 
  made 
  of 
  horizontal 
  subaerial 
  flows, 
  ejected 
  

   before 
  the 
  upturning 
  of 
  the 
  sandstone 
  ; 
  and 
  the 
  more 
  western 
  

   he 
  has 
  regarded 
  as 
  horizontally 
  ejected 
  and 
  subsequently 
  up- 
  

   turned, 
  although 
  admitted 
  to 
  be 
  interstitial 
  intrusions. 
  Neither 
  

   ' 
  of 
  these 
  conclusions 
  are 
  sustained 
  by 
  the 
  facts 
  which 
  have 
  been 
  

   presented. 
  

  

  The 
  facts 
  prove 
  further 
  that 
  the 
  era 
  of 
  disturbance 
  or 
  of 
  the 
  

   upturning 
  of 
  the 
  sandstone 
  was 
  not 
  due 
  iri 
  any 
  way 
  to 
  the 
  

   ejection 
  or 
  heat 
  of 
  the 
  igneous 
  rock. 
  The 
  latter 
  event, 
  

   although 
  so 
  extensive, 
  was 
  simply 
  incident 
  to 
  the 
  disturb- 
  

   ance 
  ; 
  the 
  upturning 
  preceded 
  the 
  eruptions. 
  

  

  Effects 
  of 
  Obstructions 
  to 
  the 
  outflow. 
  — 
  Although 
  the 
  trap 
  

   of 
  West 
  Rock 
  — 
  that 
  is 
  of 
  the 
  southern 
  part 
  of 
  the 
  West 
  Rock 
  

   ridge 
  — 
  is 
  not 
  divided 
  into 
  several 
  areas, 
  other 
  effects 
  of 
  obstruc- 
  

   tions 
  may 
  be 
  looked 
  for, 
  since 
  the 
  hanging 
  wall 
  of 
  a 
  large 
  inclined 
  

   fissure 
  is 
  sure 
  to 
  have 
  its 
  downfalls. 
  The 
  gaps 
  or 
  notches 
  in 
  

   the 
  ridge 
  indicate 
  incipient 
  division, 
  and 
  may 
  be 
  among 
  the 
  

   effects 
  from 
  such 
  a 
  cause. 
  They 
  may 
  have 
  been 
  produced 
  also 
  

   by 
  local 
  narrowings 
  of 
  the 
  fissure 
  through 
  horizontal 
  or 
  oblique 
  

   movement 
  of 
  its 
  walls, 
  or 
  in 
  other 
  ways 
  ; 
  and 
  it 
  is 
  a 
  question 
  

   whether 
  the 
  results 
  of 
  these 
  two 
  modes 
  of 
  origin 
  can 
  be 
  dis- 
  

  

  * 
  This 
  Journal, 
  vol. 
  xxxviii, 
  p. 
  361, 
  1889. 
  

  

  