﻿J. 
  F. 
  Kemp 
  — 
  Peridotite 
  Dikes 
  near 
  Ithaca, 
  JV. 
  Y. 
  411 
  

  

  northeast 
  of 
  Ithaca 
  and 
  seventy-five 
  miles 
  from 
  Syracuse, 
  but 
  

   what 
  its 
  character 
  is 
  or 
  whether 
  it 
  is 
  indeed 
  igneous 
  is 
  unknown 
  

   to 
  the 
  writer. 
  

  

  The 
  dike 
  in 
  Six 
  Mile 
  Creek 
  near 
  Ithaca 
  was 
  re-located 
  in 
  

   1887, 
  and 
  slides 
  were 
  at 
  once 
  prepared. 
  It 
  proved 
  to 
  be 
  

   a 
  thin 
  mass 
  1J 
  to 
  2 
  inches 
  wide 
  and 
  fills 
  one 
  of 
  the 
  numerous, 
  

   parallel, 
  north 
  and 
  south 
  joints 
  which 
  are 
  extremely 
  abundant 
  

   in 
  the 
  shaly 
  sandstones 
  of 
  the 
  region. 
  It 
  crosses 
  the 
  stream 
  

   like 
  a 
  narrow 
  ribbon 
  and 
  pinches 
  out 
  a 
  few 
  feet 
  above 
  the 
  sur- 
  

   face 
  of 
  the 
  water. 
  It 
  has 
  a 
  light 
  brown 
  or 
  drab 
  color 
  with 
  

   darker 
  spots 
  scattered 
  through 
  and 
  is 
  provided 
  with 
  numerous 
  

   scales 
  of 
  a 
  reddish 
  mica. 
  It 
  effervesced 
  and 
  in 
  the 
  slides 
  

   showed 
  a 
  mass 
  of 
  alteration 
  products 
  with 
  very 
  strong 
  sug- 
  

   gestions 
  of 
  an 
  eruptive 
  structure, 
  but 
  as 
  the 
  material 
  was 
  so 
  

   decomposed 
  it 
  was 
  decided 
  to 
  be 
  too 
  meagre, 
  to 
  deserve 
  men- 
  

   tion. 
  It 
  was 
  subsequently 
  submitted 
  to 
  Messrs. 
  Gr. 
  H. 
  Wil- 
  

   liams, 
  Diller 
  and 
  Derby 
  and 
  the 
  last 
  two 
  were 
  strongly 
  of 
  the 
  

   opinion 
  that 
  it 
  was 
  igneous 
  and 
  suggested 
  blasting. 
  Later 
  dis- 
  

   coveries 
  make 
  this 
  procedure 
  hardly 
  necessary 
  and 
  prove 
  the 
  

   specimen 
  to 
  be 
  undoubtedly 
  an 
  eruptive 
  rock 
  in 
  advanced 
  

   decomposition. 
  

  

  During 
  a 
  visit 
  from 
  Professor 
  Derby, 
  the 
  past 
  autumn, 
  the 
  

   subject 
  of 
  dikes 
  was 
  again 
  brought 
  up 
  and 
  the 
  probable 
  loca- 
  

   tion 
  of 
  one 
  in 
  Cascadilla 
  Creek 
  was 
  indicated. 
  The 
  point 
  is 
  

   under 
  the 
  discharge 
  raceway 
  of 
  the 
  reservoir 
  forming 
  Willow 
  

   pond, 
  just 
  east 
  of 
  the 
  entrance 
  to 
  the 
  Cornell 
  Campus. 
  In 
  a 
  

   recent 
  drouth 
  it 
  became 
  accessible. 
  The 
  dike 
  is 
  about 
  three 
  

   feet 
  in 
  width 
  and 
  strikes 
  north 
  and 
  south 
  right 
  across 
  the 
  

   course 
  of 
  the 
  creek. 
  It 
  is 
  in 
  a 
  recess 
  formed 
  by 
  its 
  weather- 
  

   ing 
  and 
  a 
  corresponding 
  recess 
  appears 
  on 
  the 
  opposite 
  side, 
  

   filled 
  however 
  with 
  dirt. 
  It 
  is 
  covered 
  with 
  sand 
  in 
  the 
  creek. 
  

  

  The 
  rock 
  itself 
  is 
  very 
  dark 
  green 
  to 
  black. 
  Its 
  surface 
  is 
  

   mottled 
  by 
  black 
  protuberances 
  which 
  look 
  very 
  much 
  as 
  if 
  

   they 
  were 
  pebbles. 
  But 
  they 
  readily 
  crumble 
  under 
  the 
  

   fingers 
  to 
  a 
  black 
  dirt. 
  The 
  fresher 
  portions 
  have 
  a 
  porphy- 
  

   ritic 
  aspect 
  and 
  suggest 
  a 
  peridotite 
  at 
  once, 
  and 
  this 
  is 
  verified 
  

   by 
  the 
  slides. 
  In 
  the 
  sections 
  the 
  rock 
  is 
  seen 
  to 
  be 
  highly 
  

   altered. 
  The 
  black 
  masses 
  prove 
  to 
  be 
  the 
  remains 
  of 
  large 
  

   olivine 
  and 
  enstatite 
  or 
  bronzite 
  crystals. 
  

  

  The 
  latter 
  show 
  very 
  generally 
  the 
  striated 
  appearance 
  so 
  

   characteristic 
  of 
  these 
  pyroxenes 
  but 
  the 
  silicate 
  itself 
  has 
  

   changed 
  to 
  serpentine 
  and 
  carbonates. 
  The 
  crystals 
  are 
  8-5 
  mm 
  

   in 
  diameter. 
  The 
  recognizable 
  olivine 
  is 
  in 
  smaller 
  crystals 
  

   than 
  the 
  pyroxene 
  as 
  a 
  general 
  thing, 
  but 
  appears 
  in 
  no 
  incon- 
  

   siderable 
  amount. 
  It 
  is 
  very 
  probable 
  that 
  the 
  larger, 
  unstri- 
  

   ated 
  alteration 
  masses 
  were 
  also 
  olivine. 
  The 
  characteristic 
  

   reddish 
  biotite 
  of 
  the 
  peridotites 
  is 
  distributed 
  through 
  the 
  

  

  