482  FEE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
metamorphosed  eruptives.  While  the  major  portion  of  granite- gneiss 
and  associated  rocks  were  considered  older  than  the  oldest  elastics,  later 
intrusives  of  a  similar  character  were  recognized.  This  theory  that 
the  fundamental  complex  is  igneous  is  that  of  Geikie  as  to  the  major 
part  of  the  Archean  of  Great  Britain  and  that  of  many  German  geolo- 
gists as  to  the  basal  complex  of  Germany,  among  whom  Lehmann  and 
Roth  are  conspicuous.  In  deed,  these  1  ast  two  ma  intain  the  igneous  origin 
of  all  the  pre- Cambrian  rocks,  and  Geikie  says  of  the  true  Archean  of 
Great  Britain  that  with  certain  possible  exceptions  it  not  only  contains 
no  material  which  gives  any  evidence  of  ever  having  been  sedimentary 
material  of  any  kind,  but  it  farther  contains  no  material  which  can  be 
considered  a  surface  volcanic,  while  in  it  there  are  many  rocks  which 
are  certainly  plutonic  eruptives. 
The  geologists  of  this  third  school,  with  the  second  school,  recognize 
the  igneous  character  of  the  granite- gneisses  having  irruptive  contacts 
with  the  clastic  series,  but  they  decline  to  recognize  these  rocks  as 
Archean.  Such  rocks  are  eruptives.  Their  age  is  to  be  designated 
precisely  as  are  eruptive  rocks  which  cut  Cambrian ,  Silurian,  or  De- 
vonian strata. 
As  bearing  in  favor  of  the  really  igneous  character  of  the  Archean  is 
the  fact  that  no  case  has  been  demonstrated,  except  possibly  that  of 
the  marbles,  of  the  production  of  a  perfectly  massive  crystalline  rock 
from  a  clastic  without  intervening  fluidity.  Metamorphism,  whether 
the  original  rock  is  a  massive  eruptive  or  a  stratified  sedimentary,  pro- 
duces a  laminated  or  schistose  rock.  If  a  granitic  structure  can  be 
taken  as  evidence  of  eruptive  origin,  and  we  know  many  eruptive  rocks 
do  have  such  a  texture,  a  very  strong  case  can  be  made  for  the  erup- 
tive origin  of  the  larger  part  of  the  fundamental  complex.  The  line 
of  argument  is  precisely  analogous  to  that  by  which  the  whole  has  been 
held  to  be  sedimentary.  There  are  complete  gradations  from  the  most 
completely  schistose  and  laminated  phases  to  the  most  massive  phase. 
Also  bearing  in  favor  of  a  truly  igneous  character  for  the  basal  com- 
plex is  the  fact  that  the  rocks  referred  in  the  first  part  of  this  section 
to  the  Archean  are  more  nearly  simulated  by  igneous  rocks  which  have 
irruptive  contacts  with  ancient  elastics  than  by  any  recognizable  meta- 
morphosed sedimentaries.  In  this  connection  may  be  mentioned  the 
occurrences  in  the  Appalachians  and  in  British  Columbia  of  relations 
between  granitic  rocks  and  strata  as  late  as  the  Carboniferous  orTrias- 
sic,  analogous  to  those  which  often  prevail  between  the  granite  and 
granite-gneiss  and  the  pre- Cambrian  crystalline  schists.  Here  the  one 
class  of  rock  is  known  to  be  sedimentary,  the  other  intrusive.  It  may 
be  said  that  the  actual  gradations  between  the  Algonkian  and  Archean* 
in  certain  places  are  evidence  that  the  latter  are  not  igneous  rocks  earlier 
than  the  former;  that  gradations  can  be  explained  between  subsequent 
intrusives  and  elastics,  but  not  between  igneous  rocks  and  sedimentaries 
of  later  age.     It  has,  however,  been  shown  that  as  a  consequence  of 
