LAKE    SUPERIOR   REGION.  231 
biotite-hornblende  granite  of  eruptive  origin,  and  is  assigned  to  the 
Laurentian. 
Winchell  (N.  H.),19G  in  1897,  presents  some  additional  points  on 
the  geology  of  northeastern  Minnesota. 
The  Laurentian  includes,  in  Minnesota,  an  acidic  crystalline  schist 
of  sedimentary  origin,  and  a  massive  igneous  rock,  although  the  igne- 
ous rock  is  younger  than  the  crystalline  schist  portion  and  should 
have  a  different  designation.  The  conclusions  reached  are  that  (1) 
the  sedimentary  Laurentian  is  a  crystalline  condition  of  sedimentary 
strata,  which  are  conformably  a  portion  of  the  sedimentary  schists; 
(2)  the  igneous  Laurentian  is  the  result  of  a  more  intense  meta- 
morphism,  carried  even  to  fusion  of  some  strata.  These  conclusions 
result  particularly  from  the  study  of  a  section  from  Tower  north- 
ward, through  Vermilion  Lake,  and  of  an  area  on  the  west  side  of 
Outlet  Bay,  in  the  corners  of  sees.  13,  14,  21,  and  32,  T.  63  N.,  K.  17 
W.,  and  along  the  shore  for  one-half  mile  westward. 
It  is  evident  that  the  Stuntz  conglomerate  on  the  south  shore  of 
Vermilion  Lake  is  a  true  water-deposited  conglomerate,  of  the  same 
formation  as  the  slates  and  graywackes  of  the  district,  the  con- 
glomerate grading  into  the  quartzite  and  graywacke,  and  this  into 
argillaceous  slate.  Furthermore,  as  supposed  by  Van  Hise,  the  con- 
glomerate lies  unconformable  on  the  iron-bearing  formation  and  con- 
tains very  numerous  fragments  of  jaspilite.  The  position  of  this 
unconformity,  whether  at  the  base  of  the  Taconic  or  lower,  is  not 
ascertained. 
The  nature  and  position  of  the  conglomerate  in  the  valley  of  the 
Puckwunge,  a  small  stream  entering  Pigeon  River  north  of  Grand 
Portage,  arc  discussed.  This  conglomerate  is  overlain  by  igneous  rocks 
resembling  the  traps  of  the  Keweenawan.  The  subjacent  formation 
can  not  be  certainly  determined,  but  in  the  same  locality,  at  a  lower 
level,  is  a  slate  rock,  called  the  Puckwunge  slate,  which  was  followed 
for  some  distance  north  and  east,  and  which  is  probably  an  upper 
member  of  the  Animikie,  not  before  individualized.  The  conglom- 
erate contains  quartzite  pebbles,  which  are  referable  to  the  quartz- 
ites  of  the  Animikie,  farther  north.  It  may  be  inferred  that  this  is 
the  basal  conglomerate  of  Keweenawan,  which  has  been  identified  up 
to  Grand  Portage  Island  and  at  intervals  along  the  Lake  Superior 
coast  from  Baptism  River  to  near  Beaver  Bay. 
Berkey,  in  1897  and  1898,  describes  the  geology  of  the  St.  Croix 
Dalles.     See  summary  in  section  2,  northern  Wisconsin,  page  192. 
Winchell  (N.  H.),107  in  1898,  attempts  to  explain  the  origin  of  the 
Archean  igneous  rocks.  From  field  evidence  and  petrographic  dis- 
criminations and.  associations,  it  is  believed  that  the  alkaline  magma 
from  which  the  igneous  rocks  were  derived  is  the  result  of  aqueo- 
