234  PRE-CAMBRIAN   GEOLOGY    OF    NORTH   AMERICA. 
found  in  the  Keweenawan  at  several  points  between  Duluth  and 
Grand  Portage  have  led  to  the  conclusion  that  the  Keweenawan  may 
be  divided  into  two  great  series,  separated  by  conglomerate  and  quart  - 
zite  which  reach  a  thickness  of  several  hundred  feet.  The  lower  series 
has  been  included  in  the  Norian,  and  the  upper  series,  comprising  the 
sedimentaries  and  the  eruptives  above  them,  has  been  called  Kewee- 
nawan, the  Keweenawan  forming  the  lower  division  of  the  Cambrian. 
Grant,201  in  1898,  sketches  the  geology  of  the  eastern  end  of  the 
Mesabi  iron  range  in  Minnesota,  including  T.  64  N.,  Rs.  3  and  4  W., 
and  parts  of  lis.  2  and  5  W.,  with  some  adjacent  portions  of  Ontario. 
The  rocks  can  be  separated  into  three  divisions.  The  chief  one  of 
these  is  the  Animikie  series,  containing  the  iron-bearing  rocks  of  the 
Mesabi  range.  Older  than  the  Animikie  is  a  series  of  granites,  green- 
stones both  massive  and  schistose,  conglomerates,  slates,  and  other 
clastic  rocks,  called  the  pre- Animikie.  Younger  than  the  Animikie 
are  some  diabase  sills  and  the  great  gabbro  mass  of  northeastern  Min- 
nesota. 
Of  the  pre- Animikie  rocks,  the  greenstones  and  clastic  rocks  have 
been  called  Keewatin.  As  the  greenstones  are  usually  associated  with 
the  Mesabi  iron-bearing  rocks,  these  alone  of  the  Keewatin  rocks  are 
described.  They  lie  to  the  north  of  the  iron-bearing  rocks,  in  T.  65 
N.,  R.  5  W.,  and  extend  eastward  to  the  center  of  T.  65  N.,  R.  4  W., 
where  they  disappear  under  the  Animikie  strata.  In  general  the 
greenstones  are  at  present  diorites;  originally  some  were  certainly 
diabases,  others  were  of  the  nature  of  andesites,  and  a  large  part  were 
diorites,  or  possibly  gabbros.  At  places,  especially  along  the  east 
side  of  sec.  27,  T.  65  N.,  R.  5  W.,  the  greenstones  contain  angular  and 
subangular  fragments  of  rock  almost  like  themselves,  and  some  may 
be  regarded  as  composed  of  fragmental  volcanic  rocks.  Associated 
with  the  greenstones,  especially  in  sees.  22,  23,  and  24,  T.  65  N.,  R.  5 
W.,  are  small  masses  of  more  acidic  rocks,  quartz  porphyries  and 
quartzless  porphyries,  which  are  probably  younger  than  the  green- 
stones. 
The  pre- Animikie  granite  has  its  typical  development  on  the  shores 
of  Saganaga  Lake.  In  a  number  of  places  it  may  be  seen  in  intru- 
sive relations  with  the  greenstone.  A  quarter  of  a  mile  south  of  the 
northeast  corner  of  sec.  23,  T.  65  N.,  R.  5  W.,  many  granite  dikes 
cutting  the  greenstone  are  seen,  and  on  the  south  shore  of  West  Sea- 
gull Lake  granite  dikes  of  the  same  nature  as  the  immediately  adja- 
cent main  mass  of  Saganaga  granite  are  seen  cutting  the  greenstone. 
Both  granite  and  greenstone  are  cut  by  another  series  of  finer  grained, 
more  acidic  granite  dikes. 
The  Animikie  rocks  rest  unconformably  upon  the  pre- Animikie 
rocks,  and  usually  on  the  southern  slope  of  the  Giants  range,  which 
is  composed  essentially  of  granite.     The  strike  is  approximately  east- 
