200  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
as  the  Lake  Superior  Cupriferous  is  Cambrian  or  Lower  Silurian, 
it  is  inferred  that  the  so-called  Upper  Laurentian,  containing  Eozoon 
canadense,  is  really  Cambrian  or  Lower  Silurian. 
Winchell  (N.  H.),147  in  1882,  continues  his  description  of  locali- 
ties. At  Fond  du  Lac  the  detailed  succession  of  sandstones  and  shales 
is  given.  The  flint  and  jasper  formations  of  Gunflint  Lake  appear  to 
be  in  apparent  unconformity  with  the  underlying  slates  and  syenites. 
On  Ogishki  Manissi  Lake  is  found  a  great  conglomerate.  This  con- 
glomerate carries  large  rounded  pieces  of  the  Saganaga  granite, 
which  proves  the  greater. age  of  that  granite  and  the  uncomformity 
to  it  of  the  conglomerate.    The  conglomerate  also  contains  red  jasper. 
The  descending  succession  in  northeastern  Minnesota  is  (1)  the 
horizontal  quartzites  and  slates  running  froni  Grand  Portage  to  Gun- 
flint  Lake;  (2)  the  conglomerate;  (3)  jaspery  and  calcareous  Gun- 
flint  beds;  (4)  gray  marble;  (5)  the  tilted  slaty  Ogishki  Manissi 
conglomerate;  (6)  amphibolitic  and  chloritic  slates;  (7)  mica  schists 
alternating  with  syenite;  (8)  syenites  and  granites  of  Saganaga  and 
Gull  lakes.  Whether  the  Gunflint  beds  belong  with  the  schistose  and 
tilted  slates  and  conglomerates  of  Ogishki  Manissi  Lake  is  an  open 
question,  although  there  are  several  things  which  indicate  that  they 
belong  to  the  same  series.  The  gabbro  is  found  to  have  a  widespread 
extent.  It  is  suggested  that  if  this  gabbro  and  the  associated  red 
gneisses  belong  to  the  Cupriferous,  the  Minnesota  and  Wisconsin 
quartzites,  as  well  as  the  red  gneisses  of  the  upper  Mississippi  Valley, 
may  also  belong  to  this  series.  The  red  syenite  of  Beaver  Bay  is  a 
metamorphosed  conglomerate  which  was  brecciated  and  mingled  with 
the  trap.  This  red  rock  was  fluidized  so  as  to  intrude  itself  in  the 
form  of  belts  and  veins.  A  conglomerate  at  Taylors  Falls,  on  the  St. 
Croix,  contains  waterworn  bowlders  and  traps  of  the  region,  but  the 
superposition  of  the  conglomerate  on  the  trap  can  not  actually  be 
seen.  This  sandstone  is  fossiliferous.  It  is  concluded  that  the  Pots- 
dam is  represented  by  the  copper-bearing  series,  while  the  underlying 
Animikie  is  equivalent  to  the  Taconic  of  Emmons. 
LTpham,148  in  1884,  describes  the  crystalline  rock  outcrops  in  cen- 
tral Minnesota. 
Chester,149  in  1884,  describes  the  rocks  of  the  Mesabi  and  Ver- 
milion iron  ranges.  The  slates  and  schists  on  the  south  side  of  the 
Mesabi  range  are  nearly  horizontal.  The  rocks  here  found  are  pre- 
cisely like  those  of  the  Penokee  region  of  Wisconsin,  and  the  two 
series  bear  the  same  relation  to  the  Huronian  series.  The  iron  ore 
at  Vermilion  Lake  is  found  in  connection  with  jaspar  and  quartzite 
and  is  intimately  bedded  with  the  country  rock,  chiefly  sericite  schist, 
standing  in  a  nearly  perpendicular  position.  These  rocks  are  the 
representative  of  the  Michigan  and  Wisconsin  iron  deposits,  and  there 
is  no  doubt  that  they  belong  to  the  Huronian.     The  Vermilion  de- 
