van  hise.]  EASTERN    UNITED    STATES.  0(J7 
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),124  in  1886,  in  describing  the  building  stones,  includes 
in  the  Laurentian  rocks  the  granitic,  syenitic,  and  gneissoid  rocks,  as 
well  as  the  crystalline  marbles  which  are  everywhere  interstratifled  with 
the  gneiss  rocks,  but  usually  form  a  small  proportion  of  the  entire  mass. 
Williams,125  in  1886, 1887,  and  1888,  describes  the  peridotites,  norites, 
gabbros,  and  diorites  of  the  Oprtlandt  series  and  their  relations  to  the 
mica-schists  and  limestones.  They  are  regarded  as  eruptive  rocks  be- 
cause they  have  the  structure  and  mineralogical  composition  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  limestones ;  because  frag- 
ments of  crystalline  schist  and  limestone  are  found  inclosed  within  the 
massive  rocks;  and  because  contact  phenomena  are  found  in  the  crys- 
talline schists  and  limestones  adjoining  them. 
Britton,126  in  1887,  describes  the  serpentine  of  Staten  island  as  a 
stratified  rock  probably  derived  by  the  extensive  alterations  of  lime- 
stones. This  serpentine  appears  to  overlie  the  crystalline  limestones. 
These  metamorphic  rocks  with  the  gneisses  are  regarded  as  Archean. 
Kemp,127  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,128  in  1890,  agrees  with  Britton  that  the  basal  member  of 
the  pre-Oambrian  of  southeastern  New  York  and  New  Jersey  is  a  grani- 
toid hornblende- gneiss,  which,  is  followed  by  a  second  member,  the  iron- 
bearing  group,  and  this  in  turn  by  the  schistose  group.  The  thick- 
ness of  the  pre-Oambrian  rocks  in  the  Hudson  river  valley  is  between 
2,300  and  2,800  feet.  They  are  unconformably  below  the  Cambrian 
quartzite  and  nothing  more  definite  can- be  predicted  as  to  their  age. 
These  rocks  display  a  number  of  anticlines,  two  of  which  are  those  at 
Fishkill  and  the  Storm  King.  In  the  synclinal  trough  between  are  the 
rocks  of  the  iron-bearing  group.  The  metamorphic  strata  of  New  York 
and  Westchester  counties,  called  the  Manhattan  group,  are  divided  into 
several  divisions  from  the  base  upward,  as  follows :  (1)  Yonkers  gneiss 
which  is  an  arkose-gneiss;  (2)  Fordham  gneiss,  a  quartzite-gneiss;  (3) 
Inwood  limestone;  and  (4)  Manhattan  mica-schists.  The  age  of  the 
M auhattan  group  has  not  been  determined,  but  it  is  thought  to  be  pre- 
Cambrian.  This  group  and  the  Lower  Cambrian  sandstone  are  t>oth 
found  to  lie  on  the  second  or  iron-bearing  member  of  the  pre-Oambrian 
formation,  and  no  unconformity  has  been  found  between  the  Manhat- 
tan group  and  the  underlying  pre-Oambrian  beds.  Of  equal  signifi- 
cance is  the  lack  of  unconformability  between  the  Lower  Silurian  strata 
of  Peekskill  hollow,  Tompkins  cove,  and  Verplanks  point  with  the  par- 
tially metamorphic  beds  of  the  Manhattan  group. 
