﻿410 
  J. 
  F. 
  Kemp 
  — 
  Peridotite 
  Bikes 
  near 
  Ithaca, 
  JV. 
  Y. 
  

  

  Aet. 
  XLIII. 
  — 
  Peridotite 
  Dikes 
  in 
  the 
  Portage 
  Sandstones 
  

   near 
  Ithaca, 
  N. 
  Y.; 
  by 
  J. 
  F. 
  Kemp. 
  

  

  In 
  the 
  valuable 
  paper 
  on 
  the 
  peridotite* 
  at 
  Syracuse, 
  N. 
  Y. 
  

   which 
  appeared 
  in 
  this 
  journal 
  in 
  August, 
  1887, 
  the 
  follow- 
  

   ing 
  statement 
  is 
  made 
  and 
  it 
  doubtless 
  expresses 
  a 
  very 
  wide- 
  

   spread 
  and 
  general 
  impression. 
  " 
  This 
  rock 
  is 
  interesting 
  

   as 
  being 
  the 
  only 
  known 
  instance 
  of 
  igneous 
  intrusion 
  in 
  the 
  

   unaltered 
  and 
  undisturbed 
  Palaeozoic 
  strata 
  of 
  New 
  York" 
  

   (p. 
  144). 
  Since 
  the 
  writer's 
  first 
  residence 
  in 
  Ithaca 
  (1886), 
  

   the 
  occurrence 
  of 
  trap 
  dikes 
  in 
  the 
  vicinity 
  has 
  been 
  a 
  sub- 
  

   ject 
  of 
  frequent 
  discussion 
  in 
  the 
  geological 
  laboratory 
  of 
  

   Cornell 
  University. 
  Conversations 
  with 
  alumni 
  who 
  were 
  

   students 
  under 
  the 
  instruction 
  of 
  Professor 
  C. 
  F. 
  Hartt 
  

   (1868-1878), 
  revealed 
  the 
  fact 
  that 
  he 
  made 
  frequent 
  men- 
  

   tion 
  of 
  them 
  and 
  created 
  the 
  impression 
  that 
  they 
  were 
  

   well 
  recognized 
  phenomena 
  in 
  two 
  of 
  the 
  neighboring 
  gorges. 
  

   They 
  do 
  not 
  appear 
  to 
  have 
  become 
  a 
  matter 
  of 
  record 
  

   except 
  in 
  two 
  cases. 
  Professor 
  O. 
  A. 
  Derby 
  (now 
  in 
  Brazil) 
  

   in 
  a 
  short 
  paper 
  in 
  the 
  Cornell 
  Review 
  (which 
  was 
  the 
  

   student 
  publication 
  of 
  that 
  date), 
  vol. 
  i, 
  p. 
  70, 
  1874, 
  entitled 
  

   " 
  Hints 
  to 
  Geological 
  Students," 
  mentions 
  a 
  number 
  of 
  locali- 
  

   ties 
  involving 
  in 
  all 
  four 
  dikes. 
  Three 
  of 
  these 
  are 
  in 
  Casca- 
  

   dilla 
  Creek 
  on 
  the 
  confines 
  of 
  the 
  university 
  and 
  the 
  fourth, 
  

   said 
  to 
  be 
  the 
  best 
  for 
  study, 
  is 
  in 
  Six-Mile 
  Creek, 
  two 
  or 
  three 
  

   miles 
  distant. 
  Professor 
  F. 
  W. 
  Simonds 
  (now 
  of 
  Texas) 
  pub- 
  

   lished 
  in 
  1877, 
  a 
  short 
  article 
  in 
  the 
  American 
  Naturalist 
  (vol. 
  

   xi, 
  p. 
  49) 
  on 
  the 
  Geology 
  of 
  Ithaca, 
  N. 
  Y., 
  and 
  vicinity. 
  The 
  

   Six 
  Mile 
  Creek 
  dike 
  is 
  again 
  mentioned 
  and 
  described 
  as 
  filling 
  

   a 
  crack 
  in 
  the 
  sides 
  of 
  the 
  gorge 
  but 
  as 
  pinching 
  out 
  before 
  it 
  

   reached 
  the 
  surface. 
  Long 
  before 
  this, 
  however, 
  in 
  1842, 
  in 
  

   the 
  Report 
  on 
  the 
  3rd 
  District, 
  N. 
  Y. 
  State 
  Survey, 
  p. 
  169, 
  

   Yanuxem 
  recorded 
  four 
  narrow 
  dikes 
  in 
  the 
  Genesee 
  slate 
  near 
  

   Ludlowville, 
  which 
  is 
  ten 
  miles 
  north 
  of 
  Ithaca. 
  The 
  locality 
  

   has 
  been 
  recently 
  visited 
  by 
  the 
  writer 
  but 
  only 
  the 
  two 
  dikes 
  

   near 
  the 
  upper 
  falls 
  of 
  Yanuxem 
  could 
  be 
  found. 
  They 
  are 
  

   each 
  about 
  an 
  inch 
  wide 
  and 
  only 
  show 
  over 
  a 
  short 
  space 
  as 
  

   they 
  disappear 
  above 
  and 
  below. 
  They 
  were 
  inaccessible 
  and 
  

   from 
  the 
  distance 
  of 
  a 
  few 
  feet 
  their 
  igneous 
  nature 
  was 
  not 
  

   conclusively 
  shown. 
  The 
  other 
  two 
  could 
  not 
  be 
  found. 
  Yan- 
  

   uxem 
  also 
  mentions 
  another 
  dike 
  (1. 
  c. 
  pp. 
  207-208) 
  at 
  Manheim 
  

   Bridge 
  east 
  of 
  Little 
  Falls, 
  N. 
  Y., 
  more 
  than 
  one 
  hundred 
  miles 
  

  

  *G. 
  H. 
  Williams: 
  The 
  Serpentine 
  (Peridotite) 
  occurring 
  in 
  the 
  Onondaga 
  Salt 
  

   Group 
  at 
  Syracuse, 
  N. 
  Y., 
  this 
  Journal, 
  August, 
  1887, 
  p. 
  144. 
  See 
  also 
  Proc. 
  Geol. 
  

   Soc. 
  Amer., 
  vol. 
  i, 
  pp. 
  533, 
  534. 
  

  

  