SOUTHEASTERN    NEW    YORK.  623 
hornblende,  Primary  limestone  and  anthophyllite  rock.  On  the  west- 
ern side  of  the  island  the  gneiss  so  abounds  with  veins  of  granite 
parallel  with  the  strata  that  in  many  places  they  constitute  the  chief 
material.  At  Kings  Bridge  the  limestone  at  its  junction  with  the 
gneiss  shows  the  structure  of  that  rock  with  the  mineral  matter  of 
limestone,  but  the  pure  limestone  is  in  beds  without  stratification. 
Mather,09  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  of  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  angle  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  Caldwell's  landing, 
and  range  south-soutlrwest  until  they  disappear  beneath  the  red  sand- 
stone formation.  The  rocks  of  this  system  have  the  same  strike  and 
dip  as  those  of  the  Champlain  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  reMs 
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  Champlain  division 
metamorphosed.  In  favor  of  this  conclusion  are  the  facts  that  the 
succession  is  the  same;  that  both  of  these  systems  are  superimposed 
upon  the  Primary  without  any  intervening  strata;  that  the  unmodi- 
fied beds  are  traced  into  those  that  are  metamorphic;  and  that  the 
places  where  the  rocks  are  most  metamorphosed  are  those  where  there 
are  intrusives  and  have  been  unheavals. 
Under  the  head  metamorphic  rocks  are  described  rocks  which  are 
not  included  in  the  foregoing  and  which,  Avhile  there  is  no  demonstra- 
tive evidence  of  it,  are  regarded  as  originally  sedimentary  rocks  that 
have  been  so  altered  as  to  change  them  into  such  rocks  as  have  usually 
been  called  Primary.  The  metamorphic  rocks  are  divided  into  those 
east  of  the  Highlands  of  the  Hudson,  and  those  of  the  Highland-  of 
Saratoga  and  Washington  counties.  In  the  lirst  district  the  lime- 
stones are  granular,  dolomitized,  and  stratified.  The  slate-  are  talco- 
argillaceous,  talcose,  chloritic,  or  micaceous,  the  last  predominating; 
and  the  sandstones  are  changed  into  granular  quartz  rock,  eurite.  and 
