202  PRE-CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA. 
Upper  Laurentian  or  Norian  of  Canada.  The  granites  and  gneisses 
show  evidence  of  metamorphic  origin.  (2)  A  mica  schist  group,  which 
is  penetrated  by  biotite  granite.  (3)  The  black  mica  slate  group, 
which  often  contains  graphitic  schists,  in  which  are  such  ore  deposits 
as  the  Commonwealth  mine  of  Wisconsin.  (4)  A  series  of  obscure 
hydromicaceous  and  greenish  magnesian  schists,  along  with  quartzites 
and  clay  slates,  with  which  are  the  more  important  bodies  of  hematitic 
iron  ores,  including  those  at  Marquette  and  the  magnetic  belt  at  Peno- 
kee.  (5)  The  great  quartzite  and  marble  group,  which  includes  the 
marble  of  Menominee  and  the  marble  and  lower  quartzite  of  Mar- 
quette, the  great  conglomerate  of  Ogishki  Manissi  Lake,  and  the  lower 
slate,  conglomerates  of  Canada.  (6)  The  granites  and  syenites  with 
hornblende  schists.  This  is  the  lowest  recognized  horizon  of  the  Lau- 
rentian. Nos.  3,  4,  and  5  together  are  the  equivalent  of  the  Taconic 
system,  3  being  the  equivalent  of  the  Animikie,  while  5  is  the  equiva- 
lent of  the  Huronian  of  Canada.  This  succession  is  compared  with 
the  successions  of  Brooks  and  Irving  in  Michigan  and  Wisconsin. 
Willis,154  in  1886,  describes  the  rock  occurrences  at  several  iron  dis- 
tricts in  northeastern  Minnesota.  At  Pokegama  Falls,  on  the  Missis- 
sippi, are  found  outcrops  of  red  quartzite  and  coarse-grained  sand- 
stone, sometimes  metamorphosed  to  a  quartzite  and  irregularly  inter- 
stratified  with  hard  specular  ore.  On  Prairie  River  is  found  granite, 
southeast  of  which  are  quartzites,  sandstone,  and  ore. 
At  Vermilion  Lake  the  iron-bearing  series  has  a  dip  of  between  85° 
and  90°,  the  structure  being  regarded  as  an  anticline,  upon  the  north 
side  of  which  is  the  Vermilion  range  and  on  the  south  side  that  of  Two 
Rivers.  The  succession  from  the  base  upward  is  as  follows :  (1)  Light- 
green,  thinly  laminated,  chloritic  schist.  (2)  Jasper  of  white,  gray, 
brown,  and  bright  red  colors,  interstratified  with  layers  of  hard  blue 
specular  ore,  which  also  occurs  in  ore  bodies  of  considerable  extent 
running  across  the  bedding;  thickness  200  to  600  feet  or  more.  (3) 
Chloritic  schist,  similar  to  1;  original  thickness  probably  about  150 
feet.  (4)  Quartzite,  dark  gray,  white,  or  black,  of  saccharoidal  tex- 
ture, containing  grains  of  magnetite  which  make  it  a  readily  recog- 
nized magnetitic  formation;  probable  thickness  200  feet.  (5)  Con- 
glomerate, consisting  of  sandstone  pebbles  and  traces  of  black  slate 
inclosed  in  siliceous  chloritic  schist.  (6)  Compact  homogeneous  rock, 
composed  of  quartz  grains,  chlorite,  hornblende,  plagioclase  feldspar, 
and  calcite.  This  rock  may  be  an  eruptive  quartz  diorite,  but  is  con- 
sidered a  metamorphosed  sedimentary  transition  bed  between  5  and  7. 
(7)  Black  clay  slate,  fissile  and  sonorous.  It  occupies  a  broad  area 
north  of  the  Vermilion  range.  In  section  28  huge  masses  of  jasper 
form  the  crown  of  the  arch  and  are  embedded  in  green  schist,  with 
which  they  agree  in  strike  and  dip,    The  jasper  blocks  are  rectangu- 
