vanhisM  DISCUSSIONS    OF    PRINCIPLES.  479 
If  this  sedimentary  view  of  the  origin  of  the  Archean  be  correct,  as  no 
universal  break  in  geological  continuity  can  be  accepted,  it  should  be 
found  that  between  the  Archean  and  the  elastics  there  are  somewhere 
gradations.  It  has  been  seen  in  the  summary  of  the  literature  that 
Hitchcock,  Marvine,  Stevenson,  King,  Winch  ell,  and  others,  accepting 
such  a  sedimentary  origin,  believe  gradations  have  been  found  in  the 
Rocky  mountain  system,  in  the  lake  Superior  region,  and  in  the  Appa- 
lachians, between  the  basal  complex  and  the  recognizable  elastics. 
These  authors  have  regarded  the  fact  that  as  a  whole  these  rocks  show 
lamination  as  evidence  that  they  were  originally  sedimentary.  A  few 
years  ago  it  was  a  matter  of  course  that  distinct  lamination  in  a  rock, 
however  faint,  is  evidence  of  sedimentation.  Lamination  being  found 
in  the  granite-gneisses,  combined  with  the  fact  that  these-  rocks  graded 
into  the  elastics,  was  taken  as  conclusive  evidence  of  the  original  sedi- 
mentary origin  of  the  whole. 
It  is  now  everywhere  recognized,  as  early  shown  by  E.  Emmons  and 
Lieber,  that  schistose  structure  is  often  produced  in  eruptive  rocks; 
also  like  structures  are  produced  in  sedimentary  rocks  which  have  no 
relation  to  the  original  lamination,  as  early^  noted  by  Tyson,  E.  Em- 
mons, Blake,  Adams,  E.  Hitchcock,  Jackson,  Jukes,  Eogers,  and 
Lieber.  E.  Hitchcock,  E.  Emmons,  and  Lieber  traced  the  actual  grada- 
tions between  schist-conglomerates  and  crystalline  schists,  while  Mather 
traced  the  blue  fossiliferous  limestones  into  completely  crystalline  gran- 
ular marbles.  Laminated  or  schistose  structure  in  crystalline  schists 
then  bears  neither  for  not  against  a  clastic  origin. 
The  manner  in  which  the  finely  laminated  schists  and  gneisses  vary 
into  the  coarsely  granitoid  phases  has  been  admirably  described  by 
Jukes  in  the  rocks  of  Newfoundland,  by  Lieber  and  E.  Emmons  in  the 
locks  of  the  southern  Appalachians,  by  Hitchcock  in  the  rocks  of 
Massachusetts  and  Vermont,  by  Marvine  and  Stevenson  in  the  rocks 
of  Colorado,  by  King,  Hague,  and  S.  F.  Emmons  in  the  rocks  of  the 
fortieth  parallel,  and  by  Lawson  in  the  rocks  about  lake  Superior. 
Most  of  these  writers  and  many  others,  including  Selwyn,  approach- 
ing the  problem  from  the  side  of  the  clastic  rocks,  have  regarded  the 
coarsely  crystallized  rocks  as  produced  by  metaniorpkism,  although 
in  the  more  granular  rocks  the  process  has  gone  so  far  as  to  produce 
aqueo-igneous  fusion.  Those  who  have  maintained  this  origin  for 
these  rocks  have  recognized  the  fact  that  they  have  locally  acted  as 
eruptives,  although  in  general  the  material  is  thought  not  to  have  moved 
far.  Marvine  so  clearly  saw  that  the  facts  could  be  explained  in  two 
ways  that  he  says  that,  while  he  regards  the  whole  as  metamorphosed 
sedimentary  rocks,  another  observer  approaching  the  field  from  a  dif- 
ferent direction,  where  the  evidences  of  intrusive  nature  are  most  mani- 
fest, would  reach  the  conclusion  that  the  whole  is  eruptive.  Hitchcock 
and  Stevenson  and  most  of  the  others  are  in  practically  the  same  posi- 
tion. 
