ADIRONDACK    MOUNTAINS.  603 
In  the  southern  part  of  the  area  examined  is  a  granite  which  does 
not  grade  into  gneiss  and  which  breaks  through  the  limestone,  causing 
great  disturbance  in  strike  and  dip,  inclosing  masses  of  the  rock  many 
feet  in  diameter,  and  metamorphosing  this  rock  to  some  extent.  The 
sandstone  at  Gouvernenr  was  found  in  direct  contact  with  the  lime- 
stone. Here  it  appears  that  the  limestone  surface  was  subjected  to 
erosion  before  the  sandstone  was  deposited  upon  it.  In  confirmation 
of  this  are  seen  narrow  irregular  cracks  extending  several  feet  into  the 
limestone,  which  have  been  filled  with  sand-tone.  The  limestone  was 
evidently  completely  lithified  when  the  sandstone  was  deposited  and 
sifted  into  it,  and  this  implies  discordance.  This  unconformity  proves 
that  the  limestone  is  older  than  the  upper  Cambrian,  the  data  being 
wanting  for  any  more  definite  determination  of  its  age.  The  meta- 
morphism  of  the  rocks  of  the  limestone-bearing  series  occurred  before 
upper  Cambrian  time,  but  the  sandstone  is  metamorphosed,  and  this 
metamorphism  must  therefore  belong  to  post-Potsdam  time. 
Smyth,-3  in  1893,  describes  the  rocks  of  Gouvernenr,  N.  Y.  The 
gneiss  gives  evidence  of  mechanical  deformation  in  the  shattering  of 
the  quartz  and  feldspar  particles.  Within  the  feldspar,  along  the 
cracks,  microperthite  has  developed  which  does  not  show  any  dynamic 
action.  The  granite  is  much  later  than  the  gneiss,  but,  like  it,  has  to 
some  extent  suffered  from  dynamic  action.  In  general  it  is  massive, 
or  nearly  so,  but  there  are  zones  of  shearing  where  granulite  and 
gneiss  have  developed.  Also  in  one  portion  there  is  a  dark  rock  ap- 
proaching a  diorite,  into  which  the  granite  grades,  but  this  is  regarded 
as  a  basic  segregation  from  the  original  magma.  The  crystalline 
limestone  is  rather  uniform  in  character,  but  where  intruded  by  the 
granite  it  is  more  coarsely  crystalline  and  various  metamorphic  min- 
erals have  developed.  Near  the  base  of  the  limestone  is  a  pyroxenic 
rock  which  is  schistose,  highly  contorted,  and  of  somewhat  doubtful 
origin,  in  the  field  being  regarded  as  sedimentary,  and  under  the 
microscope  having  an  appearance  which  suggests  igneous  origin.  In 
this  pyroxenic  gneiss  occasionally  scapolite  is  found.  The  Potsdam 
is  a  pure  vitreous  quartzite,  indurated  by  the  process  of  cementation. 
Nason,24  in  1853,  describes  the  gneissic  rocks  bearing  iron  ore  in  the 
Adirondack  region  as  precisely  like  the  Mount  Hope  type  of  rock, 
bearing  the  New  Jersey  magnetites,  and  it  is  thought  that  the  two  are 
probably  contemporaneous  bedded  deposits.  These  gneissic  ores  are 
nontitaniferous  and  are  to  be  discriminated  from  the  titaniferous  iron 
ores  which  are  associated  with  the  labradorite  rocks  or  norites  of  the 
region.  These  in  occurrence  and  association  are  wholly  distinct  from 
the  ores  belonging  in  the  gneisses. 
Kemp  and  Marsters,25  in  L893,  give  the  held  occurrence  and  micro- 
scopical characters  of  the  trap  dikes  of  the  Lake  Champlain  region. 
