LAKE  SUPERIOR  REGION.  127 
and  having  conformable  beds  of  the  various  oxides  of  iron,  and  is 
everywhere  sharply  folded  into  narrow  troughs  and  irregular  basins 
trending  in  every  direction.  The  Laurentian  is  still  more  plicated  and 
metamorphosed,  the  stratification  often  being  entirely  obliterated. 
Whether  the  Laurentian  rocks  can  be  separated  into  two  or  more  non- 
conformable  systems,  as  in  Canada,  no  opinion  is  ventured.  Since 
Keweenaw  Peninsula  is  a  striking  geographical  feature  in  Lake  Supe- 
rior, and  is  the  locality  where  the  copper-bearing  series  is  best  ex- 
posed, the  name  Keweenawian  is  suggested  for  this  period. 
Brooks,39  in  1876,  gives  a  list  of  the  rocks  of  the  Huronian  series  in 
the  order  of  their  abundance  and  as  they  occur  in  stratigraphical  suc- 
cession in  the  Marquette,  Menominee,  Penokee,  and  Gogebic  series. 
Lithologically  the  rocks  are  divided  into  (1)  fragmental  rocks,  exclu- 
sive of  limestone;  (2)  metamorphic  rocks  not  calcareous;  (3)  calca- 
reous rocks;  (4)  igneous  rocks. 
The  fragmental  rocks  include  quartz  conglomerates,  which  occur  in 
the  middle  horizon,  in  both  the  Marquette  and  the  Menominee  and  in 
the  latter  at  the  base  of  the  series,  where  it  holds  pebbles  of  granite, 
gneiss,  and  quartz.  In  the  metamorphic  rocks  not  calcareous  are  in- 
cluded many  varieties;  the  mica-bearing  series  includes  granite,  sye- 
nite, gneiss,  mica  schists,  hornblende  schists,  mica  slates,  clay  slates, 
diorites,  diabases,  quartzites,  siliceous  schists,  chert  and  jasper  rocks, 
iron  ores,  as  well  as  many  others.  Among  the  eruptive  rocks  is  a  f eld- 
spathic  series,  including  granite  dikes;  hornblendic  and  pyroxenic 
series,  including  diabase  and  similar  rocks;  and  hydrous  magnesian 
schistose  rocks  which  are  found  in  dikelike  forms  crossing  the  quartz- 
ites, iron  ores,  and  greenstones. 
The  succession  in  the  Marquette  region  from  the  base  upward  is  (a) 
syenite,  diorite,  diabase,  hornblende  schists,  slates,  conglomeratic 
quartzites,  and  various  quartzose  iron  ores;  (b)  quartzite  graduating 
into  protogine  and  containing  interstratified  beds  of  dolomitic  mar- 
ble; (c)  ferruginous  quartzose  schist;  (d)  hornblendic  rocks  with 
greenstones;  (e)  ferruginous  quartzose  flags,  clay  slates,  and  quartz- 
ites; (/)  hornblendic  rock  related  to  diorite  and  diabase;  (g)  sili- 
ceous hematitic  and  limonitic  schistose  ores;  (h)  diorite,  hornblende 
schist,  and  chlorite  schist;  (i)  arenaceous  quartz  schist,  banded  with 
micaceous  iron  and  quartzose  limonitic  ore;  (/)  pure  specular  hema- 
tite and  magnetite,  with  banded  jaspery  schists  and  interstratified 
beds  of  chloritic  and  hydromica  schist;  (k)  an  arenaceous  quartzite, 
often  semischistose  and  conglomeratic;  (I)  argillaceous  slate;  (m) 
quartz  schists;  (n)  anthophyllitic  schist;  (o)  mica  schist.  Similar 
successions  are  given  in  the  other  regions  mentioned  and  correlated 
with  that  in  the  Marquette  region,  and  all  of  these  successions  are 
compared  and  correlated  with  Logan's  succession  in  Canada. 
