394  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
can  always  be  distinguished  from  Stockbridge  limestone;  also  other 
minerals,  such  as  spinel,  sapphire,,  idocrase,  hornblende,  pyroxene, 
ehondrodite,  and  mica,  are  found  plentifully  in  the  primary,  but  do  not 
occur  in  the  Stockbridge.  The  rocks  of  the  Taconic  system  are  in- 
verted, greatly  disturbed,  and  their  relations  with  the  underlying  and 
overlying  rocks  are  obscure,  so  that  the  true  structure  can  only  be 
ascertained  by  most  careful  examination. 
Credner,111  in  1865,  states  that  the  island  of  New  York  and  the  east 
part  of  Long  island  consist  of  gneiss,  which,  toward  the  north,  con- 
tains hornblende-gneiss,  hornblende-schist,  syenite,  and  hypersthenite, 
and  in  the  last  two  are  magnetite.  The  northern  hilly  part  of  Staten 
island  consists  of  dioritic  rocks,  of  serpentine,  with  layers  of  soap- 
stone. 
Macfarlane,112  in  1865,  describes  the  rocks  in  the  neighborhood  of 
Rossie  as  belonging  almost  exclusively  to  the  Laurentian  formation, 
which  is  here  and  there  unconformably  overlain  by  patches  of  Pots- 
dam sandstone.  The  rocks  here  found  comprise  micaceous  and  horn- 
blendic  gneiss,  mica-schist,'  gneiss-granite,  granite,  tourmaline  rock, 
coarsely  granular  saccharoidal  crystalline  limestone,  and  diorite.  The 
strata  are  in  an  almost  vertical  position. 
Stevens,113  in  1867,  describes  New  York  island  as  consisting  in  the 
main  of  gneiss,  in  which  lie  veins  and  beds  of  granite,  anthophyllite, 
and  hornblende.  The  granite  occurs  in  veins  generally  coincident  with 
the  gneiss,  but  also  in  massive  beds  which  lie  across  the  strata.  At 
times  it  is  distinctly  separated  and  in  others  insensibly  blends  into  the 
gneiss.  The  hornblende  and  anthophyllite  occur  like  the  granite. 
Limestone  occurs  at  several  points  and  is  interlaminated  and  folded 
with  the  gneiss.  This  New  York  group  of  rocks  is  like  and  regarded 
as  equivalent  to  Emmons's  Taconic.  For  it  is  proposed  the  name  Man- 
hattan group. 
Dana,78  in  1872,  describes  the  mica-schist  of  Poughquag  as  underly- 
ing conformably  the  Stockbridge  limestone.  The  mica-schist  is  under- 
lain conformably  by  the  gneiss  of  the  'Taconic  series.  Besides  the 
limestones  and  Taconic  schists  and  gneiss,  there  is  near  Poughquag, 
in  still  more  intimate  connection  with  the  quartzite  rocks  of  Azoic  age, 
a  continuation  of  the  highlands  of  New  Jersey,  which  are  probably 
Laurentian.  But  as  this  point  is  not  definitely  settled,  and  since  the 
term  Azoic  has  been  ruled  out  by  facts  proving  that  the  era  was  not 
throughout  destitute  of  life,  it  is  proposed  to  use  for  the  Azoic  era  and  its 
rocks  the  general  term  Arclttuan  (or  Archean).  These  Archean  rocks, 
coarsely  crystalline  gneisses,  are  exposed  in  a  deep  cut  on  the  Hartford 
and  Fishkill  railroad.  The  quartzite  formation  of  this  region  shows  no 
conform  ability  to  the  Archean  gneiss,  and  none  to  the  gneiss,  mica- 
schist,  or  limestone  of  the  Taconic  series.  The  nearly  horizontal  beds 
of  quartzite  lie  on  the  nearly  vertical  Archean,  and  both  occur  within 
a  few  hundred  yards  of  the  steeply  inclined  Taconic  beds. 
