﻿E. 
  0. 
  Hovey 
  — 
  Acid 
  Dike 
  in 
  the 
  Triassic 
  area. 
  287 
  

  

  Akt. 
  XXYI. 
  — 
  A 
  relatively 
  Acid 
  Dike 
  in 
  the 
  Connecticut 
  

   Triassic 
  area 
  ; 
  by 
  Edmund 
  Otis 
  Hovey. 
  

  

  During 
  the 
  years 
  1893 
  and 
  1894 
  the 
  New 
  York, 
  New 
  

   Haven 
  and 
  Hartford 
  Railroad 
  Company 
  made 
  great 
  changes 
  in 
  

   the 
  layout 
  of 
  its 
  Shore-line 
  division, 
  especially 
  in 
  the 
  eastern 
  

   part 
  of 
  the 
  town 
  of 
  JS^ew 
  Haven, 
  Conn. 
  Here 
  it 
  abandoned 
  

   its 
  old 
  route 
  entirely 
  and 
  cut 
  its 
  way 
  through 
  the 
  Triassic 
  sand- 
  

   stone 
  by 
  means 
  of 
  a 
  deep 
  trench 
  and 
  a 
  long 
  tunnel 
  nearly 
  half 
  

   a 
  mile 
  east 
  of 
  its 
  old 
  coarse. 
  For 
  a 
  considerable 
  portion 
  of 
  the 
  

   distance 
  the 
  new 
  cut 
  (50 
  feet 
  deep 
  in 
  places) 
  followed 
  a 
  shallow 
  

   valley 
  at 
  the 
  base 
  of 
  one 
  of 
  the 
  low 
  bluffs 
  of 
  sandstone 
  which 
  

   characterize 
  the 
  topography 
  of 
  the 
  region. 
  This 
  proved 
  to 
  be 
  

   one 
  of 
  the 
  numerous 
  fault 
  planes 
  of 
  the 
  district 
  and 
  the 
  sand- 
  

   stone 
  encountered 
  was 
  much 
  broken 
  and 
  slickensided, 
  so 
  much 
  

   so 
  as 
  to 
  necessitate 
  the 
  lining 
  of 
  the 
  entire 
  tunnel 
  with 
  heavy 
  

   brickwork. 
  The 
  cut 
  revealed 
  the 
  presence 
  of 
  several 
  dikes 
  

   which 
  are 
  of 
  some 
  interest. 
  All 
  of 
  them 
  are 
  transverse 
  to 
  the 
  

   strike 
  of 
  the 
  sandstone 
  and 
  the 
  three 
  largest 
  (which 
  are 
  of 
  ordi- 
  

   nary 
  diabase) 
  and 
  southernmost 
  connect 
  two 
  of 
  the 
  ranges 
  of 
  

   dikes 
  indicated 
  on 
  Percival's 
  map* 
  and 
  shown 
  in 
  more 
  detail 
  

   on 
  that 
  published 
  by 
  the 
  present 
  writer, 
  f 
  a 
  portion 
  of 
  which 
  is 
  

   reproduced 
  here, 
  with 
  additions, 
  as 
  figure 
  1. 
  The 
  two 
  smallest 
  

   dikes 
  as 
  shown 
  in 
  the 
  east 
  wall 
  of 
  the 
  cut 
  coalesce 
  in 
  the 
  floor, 
  

   appearing 
  as 
  one 
  in 
  the 
  west 
  wall 
  of 
  the 
  cut. 
  The 
  rock 
  of 
  

   these 
  is 
  different 
  from 
  the 
  diabase 
  of 
  the 
  region 
  in 
  chemical 
  

   composition 
  and 
  structure, 
  and 
  approaches 
  keratopkyre, 
  to 
  

   which 
  class 
  it 
  is 
  provisionally 
  referred. 
  Slickensided 
  surfaces 
  

   in 
  the 
  middle 
  of 
  the 
  largest 
  dike 
  (50 
  feet 
  w 
  T 
  ide) 
  show 
  that 
  some 
  

   differential 
  movements 
  in 
  the 
  region 
  have 
  acted 
  on 
  the 
  trap 
  as 
  

   well 
  as 
  the 
  sandstone. 
  

  

  The 
  relations 
  of 
  the 
  dikes 
  to 
  one 
  another 
  and 
  to 
  the 
  sand- 
  

   stone 
  are 
  so 
  clearly 
  indicated 
  by 
  the 
  accompanying 
  plan 
  (fig. 
  

   3) 
  and 
  section 
  (fig. 
  2) 
  that 
  extended 
  comment 
  on 
  this 
  feature 
  is 
  

   unnecessary. 
  The 
  dikes 
  are 
  seven 
  in 
  number, 
  but 
  Nos. 
  1 
  and 
  

   la 
  are 
  evidently 
  parts 
  of 
  the 
  same 
  ; 
  Nos. 
  2 
  and 
  3 
  probably 
  meet 
  

   a 
  little 
  east 
  of 
  the 
  cut 
  and 
  Kos. 
  4 
  and 
  4a 
  meet 
  in 
  the 
  floor 
  of 
  

   the 
  cut, 
  so 
  that 
  the 
  number 
  of 
  relatively 
  independent 
  dikes 
  is 
  

   four 
  or, 
  at 
  most, 
  five 
  (see 
  fig. 
  3). 
  They 
  vary 
  in 
  size 
  from 
  one 
  

   or 
  two 
  inches 
  up 
  to 
  about 
  fifty 
  feet, 
  and 
  extend 
  in 
  a 
  belt 
  about 
  

   440 
  feet 
  wide 
  diagonally 
  across 
  the 
  railroad 
  cut 
  from 
  northeast 
  

   to 
  southwest, 
  the 
  smallest 
  ones 
  being 
  at 
  the 
  north 
  and 
  about 
  

  

  * 
  Geol. 
  Eept. 
  of 
  Conn.. 
  1842, 
  J. 
  G. 
  Perciral. 
  "Reproduced 
  in 
  part 
  in 
  Dana's 
  

   Manual 
  of 
  Geology. 
  Fourth 
  edition, 
  p. 
  801, 
  1895. 
  

   f 
  This 
  Journal, 
  III, 
  xxxviii, 
  pi. 
  IX, 
  Nov., 
  1889. 
  

  

  