390  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
river.  This  system  consists  wholly  of  granite  arid  gneiss,  with  which 
is  associated  a  small  quantity  of  limestone  and  iron  ore.  Primary 
rocks  occur  isolated  in  the  New  York  system;  the  first  at  the  Noses  on 
the  Mohawk ;  the  second  at  the  little  falls  of  the  Mohawk ;  the  third 
at  Middleville.  With  the  Taconic  system  are  placed  a  lamellar  white 
crystalline  limestone,  with  specular  iron  ore  and  compact  red  iron  ore 
and  plumbaceous  rocks  in  Lewis  county. 
Mather,108  in  1843,  gives  a  systematic  account  of  the  geology  of  the 
first  district,  comprising  the  southern  part  of  the  state.  The  Potsdam 
sandstone  is  at  the  base  of  the  unmodified  series.  In  places  it  is  meta- 
morphic  and  has  more  or  less  the  aspect  of  gneiss  ;  at  other  times  it  is 
in  an  intermediate  state,  showing  rounded  gravel  and  sand.  The  dips 
are  usually  eastward  at  from  5°  to  20°,  but  in  the  Hudson  valley 
it  is  upturned  with  other  rocks  at  a  high  angie  toward  the  east. 
The  Taconic  system  consists  of  slates,  limestones,  and  granular  quartz 
rocks,  which  form  a  belt  of  mountainous  country  from  Vermont  to 
Peekskill  on  the  Hudson  and  a  narrow  belt  across  the  Highlands  to 
the  mouth  of  Peekskill  creek.  They  are  again  found  on  the  right  bank 
of  the  Hudson,  between  Stony  point  and  Caldwells  landing,  and  range 
south- southwest  until  they  disappear  beneath  the  red  sandstone  forma- 
tion. The  strike  and  dip  of  the  rocks  of  this  system  are  the  same  as 
those  of  the  Ghamplain  division  and  apparently  underlie  them.  The 
dip  is  in  a  general  easterly  course,  varying  from  15°  to  90°.  As  to  the 
superposition  of  the  formations  the  granular  quartz  either  rests  upon 
or  pitches  under  the  gneiss  or  granitic  rocks.  The  limestones  lie  next 
in  order  from  the  gneiss  or  granite,  either  in  super  or  sub  position,  and 
the  slates  next  follow.  This  may  be  found  difficult  of  verification,  as 
the  rocks  are  almost  universally  much  deranged  from  their  original 
position.  Many  local  details  are  described,  and  it  is  concluded  that 
the  Taconic  system  represents  the  Ohamplain  division  metamorphosed. 
In  favor  of  this  position  are  the  facts  that  the  succession  is  the  same; 
that  both  of  these  systems  are  superimposed  upon  the  primary  without 
any  intervening  strata;  the  unmodified  beds  are  traced  into  those  that 
are  metamorphic ;  and  the  places  where  the  rocks  are  most  metamor- 
phic  are  those  where  there  are  intrusives  and  have  been  upheavals. 
Under  the  head  metamorphic  rocks  are  described  such  rocks  as  are 
not  included  in  the  foregoing,  and  which,  while  there  is  no  demonstra- 
tive evidence  of  it,  are  regarded  as  originally  sedimentary  rocks,  which 
have  since  been  altered  in  their  character  so  as  to  change  them  into 
such  rocks  as  have  usually  been  called  primary.  The  metamorphic 
rocks  are  divided  into  two  divisions,  those  east  of  the  Highlands  of 
the  Hudson,  and  those  of  the  Highlands  of  Saratoga  and  Washington 
counties.  In  the  first  district  the  limestones  are  granular,  dolomitized 
and  stratified.  The  slates  are  talco- argillaceous,  talcose,  chloritic  or 
micaceous,  the  last  predominating;  and  the  sandstones  are  changed 
into  granular  quartz  rock,  eurite,  and  gneiss.     In  the  second  district 
