van  ehse,]  EASTERN    UNITED    STATES.  383 
pass  over  into  crystalline  schists.  The  descriptions  by  the  elder 
Hitchcock  of  the  way  in  which  the  schist-conglomerates  at  various 
points  pass  over  into  mica-schist  in  which  no  trace  of  the  pebbles  re- 
main are  remarkably  like  those  given  many  years  later  by  Keusch,  the 
chief  difference  being  that  in  the  latter  case  partly  destroyed  fossils 
were  found  in  the  semicrystalline  rocks.  Hitchcock's  summary  of  the 
evidence  for  the  production  of  completely  crystalline  schists  from  frag: 
mental  rocks  over  extensive  areas,  published  in  1860  in  the  Vermont 
reports,  is  demonstrative  in  its  nature.  The  case  could  hardly  be  put 
more  forcibly  at  the  present  time,  except  by  the  additional  evidence 
derived  from  microscopical  structures. 
One  of  the  most  interesting  differences  of  opinion  has  been  as  to  the 
origin  of  the  granite  and  its  relation  to  other  rocks.  The  elder  Hitch- 
cock believed  that  the  granites  and  syenites  are  produced  by  the 
aqueo-igneous  fusion  of  the  sedimentary  beds,  that  they  have  usually 
not  moved  far,  and  thus  represent  older  stratified  rocks.  Locally  it  was 
recognized  that  they  have  become  fluid  and  have  intruded  the  adja- 
cent rocks,  showing  all  the  characteristics  of  an  ordinary  eruptive. 
The  term  metamorphic  was  made  to  cover  this  once  fluid  material.  Alon^ 
the  contacts  of  the  granite  with  the  slates  and  schists,  at  various 
localities  were  found  many  rounded  fragments  which  were  taken  as  evi- 
dence of  the  metamorphic  origin  of  the  whole,  the  matrix  being  re- 
garded as  completely  fused  and  the  fragments  as  residuary  bowlders 
which  had  resisted  the  process  of  metainorphism.  Stevenson  and  Mar 
vine  interpreted  like  facts  in  the  Kooky  mountains  in  the  same  man- 
ner. These  relations  are  precisely  the  same  as  those  described  by 
Lawson  between  his  Laurentian  granite-gneiss  and  the  clastic  series 
northwest  of  lake  Superior.  The  latter  writer,  however,  declines  to 
carry  the  term  metainorphism  over  to  the  final  product  and  regards  the 
granite-gneisses  along  the  contact  zone  containing  fragments  of  the 
adjacent  rocks  as  irruptive  ones,  the  fragments  being  caught  in  the 
fluid  material  rather  than  being  a  residual  unfused  substance.  The 
emphasis  is  then  thrown  upon  the  intrusive  character  of  the  granite- 
gneiss,  a  position  less  consonant  with  the  theory  of  subcrustal  fusion 
than  that  of  Hitchcock,  Stevenson,  Marvine,  and  Winchell.  An  objec- 
tion to  the  acceptance  of  this  theory  of  the  origin  of  granite  and  gran- 
ite-gneiss is  that  it  is  one  that  is  not  easily  verifiable.  As  soon  as  a 
rock  becomes  liquid  it  does  not  longer  reveal  the  source  of  the  materia  1, 
and  the  conclusions  that  it  has  not  moved  far  and  has  been  produced 
by  the  fusion  of  the  adjacent  rocks  is  an  unproved  and  perhaps  un- 
provable assumption. 
By  Crosby  the  granites  which  cut  other  rocks  are  placed  as  the 
older;  this  conclusion  follows  from  the  hypothesis  that  the  granites  are 
metamorphic.  If  they  intrude  overlying  rooks  they  must  have  been 
produced  from  a  more  deeply  buried  series  and  are  hence  older.  Most 
geologists  interpret  these  relations  to  mean  that  the  granite  is  a  later 
