﻿412 
  J. 
  F. 
  Kemp 
  — 
  Peridotite 
  Dikes 
  near 
  Ithaca, 
  N. 
  Y. 
  

  

  rock, 
  and 
  is 
  still 
  quite 
  fresh. 
  The 
  crystals 
  run 
  about 
  0-2-O3 
  mm 
  

   long. 
  Their 
  distribution 
  indicates 
  at 
  times 
  an 
  excellent 
  flow- 
  

   structure. 
  Magnetite 
  is 
  abundant 
  both 
  in 
  irregular 
  grains 
  and 
  

   rude 
  crystals. 
  A 
  small 
  amount 
  of 
  a 
  reddish 
  brown 
  mineral, 
  of 
  

   high 
  index 
  but 
  not 
  entirely 
  isotropic, 
  is 
  also 
  present. 
  It 
  is 
  

   probably 
  perofskite. 
  The 
  groundmass 
  consists 
  in 
  large 
  part 
  

   of 
  numerous 
  small 
  acicular 
  crystals 
  of 
  highly 
  inclined 
  extinct- 
  

   ion 
  which 
  are 
  augite. 
  The 
  groundmass 
  seems 
  originally 
  to 
  

   have 
  been 
  glassy. 
  An 
  analysis 
  which 
  was 
  kindly 
  made 
  in 
  the 
  

   chemical 
  laboratory 
  at 
  Cornell 
  by 
  Mr. 
  W. 
  II. 
  Morrison, 
  grad- 
  

   uate 
  student 
  in 
  chemistry 
  yielded 
  the 
  following 
  results. 
  

  

  Si0 
  3 
  Fe 
  2 
  3 
  A1 
  2 
  3 
  CaO 
  MgO 
  K 
  2 
  Na 
  2 
  Loss 
  Total. 
  

  

  2/2 
  37-44 
  11-92 
  28-60 
  5-45 
  1-97 
  1-02 
  0-97 
  12-67=100-04 
  

  

  The 
  analysis 
  shows 
  at 
  once 
  the 
  advanced 
  stage 
  of 
  the 
  decom- 
  

   position 
  and 
  yet 
  indicates 
  a 
  very 
  basic 
  rock. 
  Qualitative 
  tests 
  

   failed 
  to 
  show 
  chromium. 
  

  

  The 
  rock 
  resembles 
  very 
  closely 
  the 
  Syracuse 
  serpentine 
  

   described 
  by 
  Dr. 
  Gr. 
  H. 
  Williams 
  in 
  its 
  general 
  macroscopic 
  ap- 
  

   pearance 
  and 
  in 
  many 
  of 
  its 
  microscopic 
  characters. 
  The 
  large 
  

   pbenocrysts 
  are 
  the 
  same 
  but 
  the 
  olivine 
  is 
  less 
  fresh 
  than 
  at 
  

   Syracuse. 
  The 
  reddish 
  mica 
  is 
  present 
  in 
  both. 
  It 
  has 
  also 
  

   been 
  compared 
  with 
  the 
  peridotite 
  from 
  Elliott 
  Co., 
  Ky.,* 
  and 
  

   that 
  of 
  Pike 
  Co., 
  Ark.,f 
  and 
  evidently 
  belongs 
  to 
  the 
  same 
  fam- 
  

   ily 
  of 
  rocks 
  but 
  as 
  might 
  be 
  expected 
  it 
  resembles 
  the 
  Syracuse 
  

   rock 
  most 
  closely. 
  

  

  The 
  occurrence 
  is 
  interesting 
  because 
  it 
  shows 
  the 
  further 
  

   distribution 
  of 
  igneous 
  rocks 
  in 
  a 
  region 
  supposed 
  to 
  be 
  free 
  

   from 
  them. 
  Ithaca 
  is 
  some 
  seventy-five 
  or 
  eighty 
  miles 
  south 
  

   of 
  Syracuse 
  and 
  much 
  higher 
  in 
  the 
  geological 
  scale. 
  The 
  

   local 
  rocks 
  are 
  shaly 
  sandstones 
  of 
  the 
  Portage 
  stage 
  and 
  are 
  

   extensively 
  seamed 
  by 
  a 
  series 
  of 
  north 
  and 
  south 
  joints 
  and 
  

   another 
  series, 
  of 
  west-northwest 
  strike. 
  The 
  dikes 
  in 
  all 
  cases 
  

   follow 
  the 
  northerly 
  series. 
  It 
  is 
  not 
  improbable 
  that 
  they 
  

   belong 
  to 
  the 
  same 
  eruptive 
  outbreak 
  that 
  found 
  a 
  larger 
  mani- 
  

   festation 
  at 
  Syracuse. 
  If 
  so 
  the 
  intrusion 
  is 
  put 
  at 
  a 
  date 
  later 
  

   than 
  the 
  Upper 
  Devonian, 
  but 
  beyond 
  this 
  no 
  further 
  deter- 
  

   mination 
  can 
  be 
  made 
  with 
  the 
  data 
  at 
  hand. 
  

  

  Geological 
  Laboratory, 
  Columbia 
  College, 
  New 
  York 
  City. 
  

  

  * 
  J. 
  S. 
  Diller: 
  The 
  Peridotite 
  of 
  Elliott 
  Co., 
  Ky. 
  Science, 
  Jan. 
  23, 
  1885, 
  p. 
  65. 
  

   Bulletin 
  No. 
  38, 
  U. 
  S. 
  G. 
  S., 
  1887. 
  

  

  f 
  Branner 
  and 
  Brackett: 
  Peridotite 
  of 
  Pike 
  Co., 
  Ark. 
  This 
  Journal, 
  July, 
  1889,. 
  

   p. 
  60. 
  

  

  