210  PKE-CAMBRTAN    GEOLOGY    OF    NORTH    AMERICA. 
Winchell  (N.  H.  and  H.  V.),167  in  1889,  maintain  that  the  iron 
ores  of  the  Keewatin  of  Minnesota  are  not  derived  from  a  carbonate, 
but  are  probably  a  direct  chemical  precipitate;  for  there  is  no  evi- 
dence of  the  existence  of  carbonate  of  iron  at  any  time,  and  the  nature 
of  the  country  rock  is  such  as  to  imply  that  no  carbonates  in  amounts 
required  could  have  been  deposited  at  the  time  the  rocks  were  formed. 
Winchell  (Alexander),168  in  1890,  repeats  his  general  conclusions 
as  to  the  stratigraphy  in  northeastern  Minnesota  and  gives  a  succes- 
sion as  follows,  in  descending  order : 
V.  Uncry stall ine  schists  (Animikie,  Huronian.). 
IV.  Semicrystalline  schists   (Keewatin). 
III.  Crystalline  schists  (Vermilion). 
II.  Gneissoid  rocks. 
I.  Granitoid  rocks   (Laurentian). 
Winchell  (K  H.  and  H.  V.),  169  in  1890,  state  that  the  iron  ores 
of  Minnesota  are  at  five  geological  horizons,  as  follows,  in  descending 
order : 
(1)  The  hematites  and  limonites  of  the  Mesabi  range,  the  equivalents  of  the 
hematites  of  the  Penokee-Gogebic  range  in  Wisconsin. 
(2)  The  gabbro  titaniferous  magnetites  near  the  bottom  of  the  rocks  of  the 
Mesabi  range. 
(3)  Olivinitic  magnetites,  just  below  the  gabbro  in  the  basal  portion  of  the 
Mesabi  rocks. 
(4)  The  hematites  and  magnetites  of  the  Vermilion  range  in  the  Keewatin 
formation. 
(5)  The  magnetites  of  the  crystalline  schists  of  the  Vermilion  formation. 
It  is  maintained  that  the  upper  iron  deposits  of  the  Mesabi  and 
those  of  the  Penokee-Gogebic  are  the  equivalents  of  the  Taconic  ores 
of  western  New  England. 
Winchell  (N.  H.),170  in  1891,  gives  numerous  additional  field  ob- 
servations. The  relations  of  the  jaspilite,  argillite,  and  green  schist 
are  considered,  and  the  argillite  at  least  is  regarded  as  a  sedimentary 
rock.  The  position  of  the  Pewabic  quartzite  is  left  uncertain.  It  is 
considered,  however,  to  overlie  the  Animikie  black  slate,  unless  there 
are  two  great  quart zites.  This  quartzite  has  heretofore  been  made 
the  parallel  of  the  great  quartzite  that  overlies  the  Animikie  uncon- 
formably,  but  it  is  possible  that  it  runs  below  it  conformably.  In 
the  Stuntz  conglomerate  is  found  a  large  boAvlder  which  contains 
pebbles  of  chalcedonic  quartz  and  quartzose  felsite  and  the  porphyrel 
at  Kekekabik  Lake.  A  study  of  the  ore  formation  leads  to  the  con- 
clusion that  all  three  of  the  known  agencies  of  rock  formation  were 
intermittently  at  work  and  concerned  in  forming  the  iron  ore,  viz: 
Eruption,  to  afford  the  basic  eruptive  material;  sedimentation,  to 
arrange  it  (in  the  main),  and  chemical  precipitation  in  the  same 
water,  to  give  the  pure  hematite  and  the  chalcedonic  silica.  The 
great  gabbro  of  the  Cupriferous  formation  is  regarded  as  lying  be- 
