﻿GEOLOGY 
  OF 
  THE 
  NORTH 
  CREEK 
  QUADRANGLE 
  3 
  1 
  

  

  markable 
  manner 
  in 
  the 
  North 
  Creek 
  region 
  gabbros. 
  In 
  the 
  ex- 
  

   amples 
  most 
  often 
  described 
  the 
  core 
  is 
  olivine, 
  but 
  in 
  the 
  gabbros 
  

   here 
  considered 
  the 
  writer 
  has 
  observed 
  cores 
  of 
  olivine, 
  hypers- 
  

   thene, 
  ilmenite, 
  augite, 
  and 
  diallage 
  with 
  from 
  one 
  to 
  five 
  distinct, 
  

   successive 
  rims 
  surrounding 
  the 
  cores. 
  Professor 
  Kemp 
  has 
  de- 
  

   scribed 
  ! 
  and 
  figured 
  a 
  number 
  of 
  interesting 
  examples 
  of 
  reaction 
  

   rims 
  observed 
  in 
  certain 
  gabbros 
  of 
  the 
  eastern 
  Adirondacks. 
  

  

  The 
  following 
  nine 
  types 
  of 
  reaction 
  rims 
  comprise 
  most 
  of 
  those 
  

   noted 
  by 
  the 
  writer 
  in 
  the 
  North 
  Creek 
  gabbros 
  : 
  

  

  1 
  Ilmenite 
  surrounded 
  by 
  hornblende. 
  

  

  2 
  Diallage 
  surrounded 
  by 
  hornblende. 
  

  

  3 
  Augite 
  surrounded 
  by 
  hornblende. 
  

  

  4 
  Hypersthene 
  surrounded 
  by 
  garnet. 
  

  

  5 
  Hypersthene 
  surrounded 
  by 
  successive 
  zones 
  of 
  biotite 
  and 
  

   hornblende. 
  

  

  6 
  Olivine 
  with 
  successive 
  zones 
  of 
  hypersthene, 
  hornblende, 
  and 
  

   garnet. 
  

  

  7 
  Olivine 
  with 
  successive 
  zones 
  of 
  hypersthene, 
  biotite, 
  and 
  garnet. 
  

  

  8 
  Hypersthene 
  with 
  successive 
  zones 
  of 
  biotite, 
  feldspar, 
  and 
  

   garnet. 
  

  

  9 
  Ilmenite 
  with 
  successive 
  zones 
  of 
  biotite, 
  hornblende, 
  garnet, 
  

   and 
  biotite. 
  

  

  In 
  nearly 
  all 
  cases 
  the 
  material 
  immediately 
  inclosing 
  the 
  rims 
  

   is 
  feldspar 
  which, 
  in 
  a 
  sense, 
  adds 
  another 
  zone 
  to 
  each 
  of 
  the 
  above. 
  

   No. 
  6 
  is 
  like 
  one 
  of 
  those 
  described 
  by 
  Kemp. 
  No. 
  9 
  is 
  a 
  remark- 
  

   able 
  example 
  and, 
  because 
  of 
  its 
  additional 
  outer 
  rim 
  of 
  biotite, 
  is 
  

   even 
  more 
  interesting 
  than 
  a 
  case 
  described 
  by 
  Lacroix. 
  2 
  Some 
  of 
  

   the 
  others 
  may 
  be 
  new 
  examples. 
  The 
  material 
  of 
  each 
  rim 
  appears 
  

   to 
  be 
  highly 
  granulated 
  or 
  at 
  least 
  made 
  up 
  of 
  numerous 
  small 
  grains. 
  

   It 
  seems 
  certain 
  that 
  where 
  hypersthene 
  envelops 
  olivine, 
  the 
  former 
  

   has 
  secondarily 
  developed 
  from 
  the 
  latter. 
  The 
  olivine 
  cores 
  are 
  of 
  

   very 
  irregular 
  shapes 
  and 
  in 
  all 
  sizes. 
  . 
  Where 
  hypersthene 
  forms 
  

   the 
  core 
  it 
  is 
  probable 
  that 
  all 
  the 
  original 
  olivine 
  has 
  been 
  altered 
  

   to 
  hypersthene. 
  The 
  common 
  occurrence 
  of 
  hornblende 
  rims 
  around 
  

   pyroxene 
  strongly 
  suggests 
  the 
  derivation 
  of 
  the 
  former 
  from 
  the 
  

   latter. 
  Garnet 
  is 
  almost 
  invariably 
  in 
  contact 
  with 
  feldspar 
  which 
  

   suggests 
  the 
  partial 
  formation, 
  at 
  least, 
  of 
  the 
  garnet 
  from 
  the 
  

   feldspar. 
  

  

  1 
  Geol. 
  Soc. 
  Amer. 
  Bui., 
  1894, 
  5 
  :2i8-2i. 
  

  

  2 
  Bui. 
  Soc. 
  Min. 
  Fr., 
  1889, 
  12:232. 
  

  

  