﻿E. 
  0. 
  Ilovey 
  — 
  Acid 
  Dike 
  in 
  the 
  Triassic 
  area. 
  289 
  

  

  110 
  feet 
  from 
  the 
  southern 
  entrance 
  to 
  the 
  tunnel, 
  which 
  passes 
  

   under 
  East 
  Grand 
  avenue 
  half 
  a 
  mile 
  east 
  of 
  the 
  Quinnipiac 
  

   river. 
  This 
  is 
  the 
  best 
  place 
  near 
  New 
  Haven 
  for 
  the 
  study 
  of 
  

   the 
  phenomena 
  of 
  dikes 
  : 
  the 
  differences 
  in 
  coarseness 
  of 
  grain 
  

   in 
  the 
  dikes 
  themselves 
  on 
  account 
  of 
  different 
  widths 
  ; 
  the 
  

   increase 
  in 
  coarseness 
  from 
  each 
  wall 
  toward 
  the 
  center, 
  espe- 
  

   cially 
  in 
  the 
  larger 
  dikes 
  ; 
  columnar 
  structure 
  perpendicular 
  to 
  

   the 
  walls 
  in 
  the 
  heavy 
  dikes 
  ; 
  inclusion 
  of 
  country 
  rock 
  in 
  the 
  

   mass 
  of 
  a 
  dike 
  and 
  the 
  effect 
  upon 
  the 
  igneous 
  rock 
  and 
  the 
  

   included 
  block; 
  contact 
  phenomena 
  on 
  sandstone 
  strata 
  of 
  

   varying 
  nature, 
  etc. 
  Two-fifths 
  of 
  a 
  mile 
  north 
  of 
  the 
  tunnel 
  

   and 
  a 
  fourth 
  of 
  a 
  mile 
  from 
  the 
  Fair 
  Haven 
  station 
  of 
  the 
  rail- 
  

   way, 
  an 
  isolated 
  dike 
  crosses 
  the 
  cut. 
  It 
  is 
  very 
  irregular, 
  

   from 
  two 
  to 
  four 
  feet 
  wide, 
  and 
  trends 
  N". 
  60° 
  W. 
  (magnetic) 
  

   and 
  hades 
  25° 
  to 
  30° 
  to 
  the 
  northeast. 
  The 
  course 
  of 
  the 
  cut 
  

   and 
  tunnel 
  is 
  N. 
  18° 
  E. 
  (Observation 
  made 
  in 
  October, 
  1894.) 
  

   The 
  dikes 
  which 
  furnish 
  the 
  rock 
  which 
  is 
  such 
  a 
  departure 
  

   from 
  the 
  normal 
  diabase 
  of 
  the 
  region 
  as 
  to 
  merit 
  special 
  

   description 
  are 
  numbered 
  4 
  and 
  4« 
  on 
  the 
  plan, 
  but 
  4& 
  appears 
  

   only 
  in 
  the 
  east 
  wall 
  of 
  the 
  cut 
  and 
  although 
  it 
  is 
  four 
  or 
  live 
  

   inches 
  wide 
  at 
  the 
  level 
  of 
  the 
  track, 
  it 
  pinches 
  out 
  about 
  fif- 
  

   teen 
  feet 
  above, 
  and 
  does 
  not 
  reach 
  the 
  surface. 
  In 
  appearance 
  

   it 
  is 
  like 
  number 
  4 
  and 
  is 
  an 
  offshoot 
  from 
  it. 
  No. 
  4, 
  from 
  

   w 
  T 
  hich 
  the 
  hand 
  specimen 
  about 
  to 
  be 
  described 
  was 
  taken, 
  

   is 
  less 
  than 
  two 
  inches 
  (45 
  mm 
  ) 
  wide 
  at 
  the 
  level 
  of 
  the 
  railway 
  

   track 
  on 
  the 
  east 
  side 
  of 
  the 
  cut 
  and 
  slowly 
  and 
  irregularly 
  

   increases 
  to 
  about 
  8 
  inches 
  in 
  width 
  toward 
  the 
  surface. 
  The 
  

   course 
  across 
  the 
  bottom 
  of 
  the 
  cut 
  is 
  about 
  1ST. 
  80° 
  W. 
  (mag- 
  

   netic) 
  and 
  its 
  hade 
  on 
  the 
  east 
  side 
  of 
  the 
  cut 
  is 
  33° 
  to 
  the 
  

   south, 
  but 
  its 
  inclination 
  changes 
  to 
  the 
  other 
  side 
  of 
  the 
  verti- 
  

   cal 
  on 
  the 
  west 
  side 
  of 
  the 
  cut 
  and 
  it 
  passes 
  very 
  irregularly 
  

   through 
  the 
  sandstone, 
  separating 
  into 
  two 
  branches 
  as 
  shown 
  

   in 
  the 
  figure 
  and 
  being 
  apparently 
  intersected 
  by 
  No. 
  5. 
  The 
  

   color 
  of 
  No. 
  4 
  near 
  the 
  bottom 
  of 
  the 
  cut 
  on 
  the 
  east 
  side 
  is 
  a 
  

   light 
  brick-red, 
  very 
  much 
  like 
  that 
  of 
  the 
  inclosing 
  sandstone 
  

   but 
  banded 
  with 
  different 
  shades 
  parallel 
  to 
  the 
  sides 
  of 
  the 
  

   dike 
  and 
  having 
  small 
  bluish 
  green 
  spots 
  (chlorite) 
  along 
  the 
  

   middle; 
  green 
  predominates 
  above. 
  On 
  the 
  west 
  side 
  the 
  dike 
  

   is 
  grayish 
  green 
  with 
  red 
  edges. 
  No. 
  4a 
  is 
  red. 
  No. 
  5 
  is 
  

   much 
  wider 
  than 
  either 
  of 
  these, 
  3 
  \ 
  feet 
  (1*1 
  meter), 
  and 
  its 
  

   color 
  and 
  appearance 
  are 
  like 
  those 
  of 
  the 
  well 
  known 
  diabase 
  

   dikes 
  of 
  the 
  region 
  : 
  a 
  very 
  dense, 
  greenish 
  black 
  rock 
  with 
  

   phenocrysts 
  of 
  augite. 
  Under 
  the 
  microscope 
  the 
  rock 
  of 
  No. 
  

   5 
  presents 
  a 
  variation 
  from 
  the 
  ophitic 
  structure, 
  of 
  typical 
  

   diabase 
  in 
  that 
  the 
  augite 
  of 
  the 
  groundmass 
  is 
  granular 
  crys- 
  

   talline 
  around 
  the 
  labradorite 
  instead 
  of 
  being 
  in 
  broad 
  plates 
  

   penetrated 
  by 
  the 
  feldspar. 
  It 
  is 
  evident 
  that 
  dikes 
  No. 
  4 
  and 
  

  

  