462  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
not  occur  in  the  Fundamental  gneiss.  The  areas  occupied  by  the 
Grenville  series,  while  together  aggregating  many  thousands  of  square 
miles,  are  probably  small  as  compared  with  those  of  the  Fundamental 
gneiss.  The  Grenville  rocks,  though  generally  highly  inclined,  over 
some  large  areas  are  nearly  horizontal,  but  even  in  these  cases  they 
have  been  subjected  to  great  pressure. 
As  to  the  origin  and  relations  of  the  Fundamental  gneiss  and  the 
Grenville  series,  three  views  may  be  taken : 
1.  The  Fundamental  gneiss  may  be  the  remains  of  a  primitive 
crust  which  was  penetrated  by  great  masses  of  igneous  rocks  and 
subjected  to  repeated  dynamic  movements.  The  Grenville  series  may 
be  an  upward  continuation  of  the  Fundamental  gneiss  under  altered 
conditions,  marking  a  transition  from  a  primitive  crust  to  normal 
sediments.  Thus  the  two  would  form  one  practically  continuous 
series.  The  general  petrographical  similarity  of  the  two  series,  taken 
in  connection  with  the  more  varied  nature  of  the  Grenville  series,  its 
frequent  stratified  character,  and  the  presence  in  it  of  limestones  and 
graphite  indicating  an  approach  to  modern  conditions  and  the  advent 
of  life,  together  with  the  difficulty  of  clearly  separating  the  two  series 
from  each  other  and  defining  their  respective  limits,  lend  support  to 
this  view. 
2.  The  Grenville  series  may  be  considered  as  distinct  from  the 
Fundamental  gneiss  and  reposing  on  it  unconformably,  being  a  highly 
altered  series  of  clastic  origin,  the  Fundamental  gneiss  having  some 
such  origin  as  suggested  above  or  being  an  older  series  of  still  more 
highly  altered  sediments.  But  as  it  is  now  thoroughly  crystalline, 
there  is  no  absolutely  conclusive  proof  that  even  the  Grenville  series 
is  of  sedimentary  origin.  However,  the  series  is  in  all  probability 
made  up,  in  part  at  least,  and  perhaps  wholly,  of  sedimentary  ma- 
terial, but  as  this  is  not  absolutely  shown,  the  proposal  to  separate  it 
from  the  rest  of  the  Laurentian  and  class  it  as  Algonkian  or  Huronian 
seems  premature. 
3.  The  Fundamental  gneiss  may  be  considered  as  a  great  mass  of 
eruptive  rock  which  has  eaten  upward  and  penetrated  the  Grenville 
series,  while  the  Grenville  series  itself  represents  a  series  of  altered 
sediments  of  Laurentian,  Huronian,  or  subsequent  age.  The  world- 
wide distribution  of  the  Fundamental  gneiss  (forming  as  it  does, 
wherever  the  base  of  the  geological  column  is  exposed  to  view,  the 
foundation  upon  which  all  subsequent  rocks  are  seen  to  rest)  is  op- 
posed to  this  view,  as  is  also  its  persistent  gneissic  or  banded  character. 
The  anorthosite  series  is  a  gabbro,  often  regularly  laminated  and 
much  altered,  which  is  intrusive  within  the  Fundamental  gneiss  and 
the  Grenville  series. 
The  Hastings  series  has  a  very  local  development.  It  consists 
largely  of  calc  schists,  mica  schists,  dolomites,  slates,  and  conglomer- 
