SOUTHEASTER X    NEW    YORK.  629 
Hudson  are  gneiss,  syenite  gneiss,  granite,  quartz  syenite,  granulite. 
and  hornblende  schist.  The  Poughquag-Fishkill  quartzite  is  found  to 
rest  unconformably  upon  the  Highland  gneisses,  the  discordance 
being  best  seen  on  the  New  York  and  New  England  Railroad,  1  mile 
west  of  West  Pawling  station.  Here  the  quartzite  has  a  dip  of  15° 
or  20°,  while  the  gneiss,  but  300  feet  distant,  has  an  almost  vertical 
inclination.  Belonging  with  the  Archean  gneisses  are  limestones, 
among  which  is  that  at  Sprout  Brook.  On  the  eastern  side  of  the 
Highlands  the  Archean  border  has  the  micaceous  schistose  rocks  and 
the  quartzites  resting  upon  it.  These  relations  are  particularly  well 
shown  at  Towner's  station.  Xear  here  the  limestones  and  schists  in 
a  syncline  rest  unconformably  upon  the  granulitic  gneiss.  Provision- 
ally the  rocks  of  the  Highlands  are  referred  to  the  Archean.  They 
may  be  all  Laurentian  also,  but  the  Huronian  has  not  been  identified. 
In  Westchester  County  is  a  great  variety  of  crystalline  rocks.  To 
these  is  applied  the  name  Manhattan  gneiss,  proposed  by  Hall.  These 
rocks  are  less  massive  than  those  of  the  Highlands,  include  micaceous 
gneiss  and  schist,  as  well  as  crystalline  limestones,  and  to  the  ordinary 
observer  are  more  like  the  common  fragmental  rocks  than  the  massive 
gray  granitoid  gneisses. 
Hall  (James),80  in  188G,  in  describing  the  building  stones,  in- 
cludes in  the  Laurentian  rocks  the  granitic,  syenitic,  and  gneissoid 
rocks,  as  well  as  the  crystalline  marbles  which  are  everywhere  inter- 
stratified  with  the  gneiss  rocks,  but  usually  form  a  small  proportion 
of  the  entire  mass. 
Williams,83  in  1886,  1887,  and  1888,  describes  the  peridotites, 
norites,  gabbros,  and  diorites  of  the  Cortlandt  series  and  their  rela- 
tions to  the  mica  schists  and  limestones.  They  are  regarded  as  erup- 
tive rocks  because  they  have  the  structure  and  mineralogical  compo- 
sition of  eruptive  types;  because  their  schistose  phases  have  nothing 
which  suggests  an  original  sedimentary  structure,  because  they  occur 
in  well-defined  dikes  in  other  massive  rocks,  in  mica  schists,  and  in 
limestones;  because  fragments  of  crystalline  schist  and  limestone  are 
found  inclosed  within  the  massive  rocks,  and  because  contact  phe- 
nomena are  found  in  the  crystalline  schists  and  limestones  adjoining 
them. 
Britton,82  in  1887,  describes  the  serpentine  of  Staten  Island  as  a 
stratified  rock  probably  derived  by  the  extensive  alteration  of  lime- 
stones. This  serpentine  appeal's  to  overlie  the  crystalline  limestones. 
These  metamorphic  rocks  with  the  gneisses  are  regarded  as  Archean. 
Kemp,88  in  1887,  describes  Manhattan  Island  as  consisting  of  a  Long 
ridge  of  gneiss,  with  Triassic  trap  and  sandstone  on  the  west  and  con- 
nected with  the  gneiss  of  the  mainland  on  the  north  and  south. 
Merrill,  si  in  L890,  agree-  with  Britton  that  the  basal  member  of 
the  pre-Cambrian  of  southeastern  New   York  and   New  Jersey  is  a 
