﻿92 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  tone 
  to 
  most 
  specimens. 
  Both 
  the 
  quartz 
  and 
  augite 
  fluctuate, 
  the 
  

   proportion 
  of 
  the 
  former 
  mineral 
  being 
  usually 
  about 
  that 
  found 
  

   in 
  a 
  moderately 
  silicious 
  granite, 
  but 
  may 
  shrink 
  to 
  very 
  small 
  

   amounts. 
  The 
  augite 
  gives 
  way 
  at 
  times 
  to 
  hornblende 
  or 
  biotite, 
  

   a 
  result 
  that 
  may 
  be 
  traced 
  in 
  part 
  to 
  secondary 
  alteration. 
  

  

  The 
  arrangement 
  of 
  the 
  constituents 
  may 
  be 
  described 
  as 
  gneiss- 
  

   oid, 
  yet 
  it 
  often 
  lacks 
  the 
  parallelism 
  of 
  typical 
  gneisses. 
  The 
  

   texture 
  is 
  mostly 
  granular, 
  such 
  as 
  would 
  be 
  produced 
  by 
  shearing 
  

   and 
  granulation 
  of 
  a 
  massive 
  rock 
  with 
  perhaps 
  a 
  certain 
  amount 
  

   of 
  flowage 
  under 
  compression. 
  Coarse 
  phases 
  in 
  which 
  little 
  crush- 
  

   ing 
  effects 
  are 
  observable 
  and 
  grading 
  into 
  a 
  pegmatite 
  rock 
  are 
  not 
  

   unusual 
  in 
  the 
  area. 
  They 
  may 
  be 
  explained 
  as 
  massive 
  aggregates 
  

   which 
  have 
  escaped 
  the 
  general 
  dynamism 
  that 
  has 
  effected 
  the 
  

   granulation 
  of 
  most 
  of 
  the 
  gneisses, 
  or 
  possibly 
  they 
  represent 
  a 
  

   recrystallization 
  of 
  the 
  latter 
  under 
  certain 
  favorable 
  conditions 
  

   which 
  have 
  obtained 
  only 
  in 
  portions 
  of 
  the 
  mass. 
  That 
  they 
  are 
  

   all 
  intrusions 
  from 
  a 
  distinct 
  magma 
  hardly 
  seems 
  possible 
  under 
  

   the 
  circumstances 
  owing 
  to 
  the 
  frequent 
  similarity 
  of 
  composition 
  

   to 
  the 
  granular 
  varieties 
  as 
  well 
  as 
  their 
  textural 
  gradation 
  into 
  the 
  

   latter. 
  On 
  the 
  whole 
  the 
  characters 
  of 
  the 
  acid 
  gneiss 
  indicate 
  its 
  

   relationship 
  to 
  the 
  granites. 
  

  

  There 
  are 
  few 
  exposures 
  of 
  sedimentary 
  types 
  among 
  the 
  

   gneisses. 
  On 
  the 
  south 
  side 
  of 
  the 
  Ausable, 
  just 
  below 
  the 
  con- 
  

   fluence 
  of 
  the 
  two 
  branches 
  at 
  Ausable 
  Forks, 
  a 
  micaceous 
  lami- 
  

   nated 
  rock 
  outcrops 
  in 
  a 
  small 
  area 
  where 
  the 
  overburden 
  of 
  sand 
  

   and 
  soil 
  has 
  been 
  washed 
  off. 
  It 
  has 
  the 
  peculiar 
  rusty 
  weathered 
  

   appearance 
  common 
  to 
  these 
  gneisses, 
  due 
  to 
  the 
  oxidation 
  of 
  

   contained 
  pyrite. 
  Some 
  layers 
  are 
  extremely 
  quartzose. 
  The 
  

   exposure 
  has 
  special 
  interest 
  from 
  the 
  fact 
  that 
  the 
  strata 
  are 
  cut 
  

   off 
  on 
  one 
  side 
  by 
  syenite 
  which 
  breaks 
  across 
  in 
  an 
  irregular 
  manner 
  

   like 
  an 
  intrusive. 
  It 
  is 
  the 
  only 
  place 
  in 
  the 
  district 
  where 
  such 
  

   evidence 
  of 
  the 
  nature 
  and 
  relative 
  age 
  of 
  the 
  syenite 
  has 
  been 
  

   found. 
  The 
  micaceous 
  gneiss 
  can 
  not 
  be 
  traced 
  for 
  any 
  distance, 
  

   as 
  the 
  river 
  and 
  its 
  deposits 
  conceal 
  the 
  outcrop. 
  The 
  elevations 
  on 
  

   the 
  opposite 
  side 
  of 
  the 
  river 
  just 
  north 
  of 
  Ausable 
  Forks 
  are 
  mostly 
  

   syenite, 
  but 
  there 
  are 
  involved 
  masses 
  of 
  amphibolite 
  and 
  of 
  a 
  light 
  

   colored 
  plagioclase 
  gneiss 
  that 
  probably 
  belong 
  to 
  the 
  sedimentary 
  

   series. 
  Crystalline 
  limestone 
  has 
  been 
  noted 
  by 
  Kemp 
  as 
  occurring 
  

   at 
  Trout 
  pond, 
  3 
  miles 
  south 
  of 
  Clintonville 
  ; 
  it 
  does 
  not 
  appear 
  to 
  

   be 
  present, 
  however, 
  anywhere 
  in 
  the 
  vicinity 
  of 
  the 
  mines. 
  

  

  The 
  strike 
  of 
  the 
  gneisses 
  varies 
  considerably, 
  but 
  is 
  mainly 
  in 
  a 
  

   northerly 
  direction. 
  The 
  common 
  readings 
  are 
  east 
  of 
  north, 
  up 
  to 
  

  

  