130  PKE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  B6. 
The  general  succession  in  descending  order  is  then  as  follows : 
Calciferous Magnesian  limestones  and  sandstones  ..} -,-v-,    ,   n     ,    ,       , 
St.  Croix Sandstones  and  shales \  Dikelocephalns  horizon 
Overlap  unconformity . 
Potsdam Quartzite,  gabbro,  red  granite,  and  Kewee- 
nawan Paradoxides  horizon. 
Overlap  unconformity. 
Taconic Black  and  gray  slates  and  quartzites,  iron 
ore  (Huronian,  Animikie) Olenellus  horizon. 
Overlap  unconformity. 
Keewatin (Including  the  Kawishiwin  or  greenstone 
belt, with  its  jaspilite),  sericitic  schists 
and  gray wackes 
Vermilion (Coiitchiching)  crystalline  schists }  Archean. 
Eruptive  unconform  ity. 
Laiuentian Gneiss 
Winchell  (H.  V.),179  in  1889,  gives  further  observations  on  the  iron 
regions  of  Minnesota.  On  the  Giant's  range  the  Animikie  is  found  to 
rest  upon  the  syenite.  Here  is  a  semicrystalline  rock  between  the 
two,  which  grades  into  the  syenite.  The  character  of  the  transition  is 
not  metainorphic,  but  rather  fraginental,  there  appearing  to  be  a  cer- 
tain amount  of  loose  crystalline  material  which  has  resulted  from  the 
decay  and  erosion  of  the  syenite  lying  on  top  of  this  rock  in  the  bed 
of  the  sea  upon  and  around  which  the  Animikie  sediments  were  de- 
posited. The  coarse  detritus  grades  up  into  the  fine  detritus  of  the 
Animikie.  The  Animikie  beds  are  found  also  to  rest  unconformably 
upon  the  upturned  edges  of  the  Keewatin  schists.  The  same  relations 
are  found  to  prevail  in  the  Birch  lake  region.  The  gabbro  containing 
ores  in  the  vicinity  of  Kawishiwi  river  are  found  to  contain  fragments 
of  the  Animikie  slates  and  quartzites,  and  is,  therefore,  of  later  origin. 
At  Gunliint  lake  the  Animikie  rests  uncomformably  upon  the  Keewatin, 
and  is  found  upon  greenstone.  The  Keewatin  schists  are  largely  of 
eruptive  origin.  The  contacts  of  the  jaspilite  with  the  basic  schists 
are  abrupt  and  angular,  and  numerous  fragments  are  found  contained  in 
the  schists.  The  jaspilite  is  regarded  as  a  sedimentary  formation  which 
was  broken  up  and  involved  in  the  eruptions  of  Keewatin  age.  The 
Huronian  quartzite  associated  with  the  magnetite,  lying  unconformably 
upon  the  syenite,  is  believed  to  lie  conformably  upon  the  Animikie  slates. 
Grant,180  in  1889,  gives  geological  observations  made  in  northeast- 
ern Minnesota.  North  of  Gunliint  lake  the  vertical  Keewatin  and  crys- 
talline schists,  with  an  east  and  west  strike,  strike  directly  across  a 
range  of  immediately  adjacent  gneisses,  the  schists  showing  no  evi- 
dence of  being  twisted  or  bent  within  200  feet  of  the  gneiss.  In  the 
syenites  of  Gunliint  lake  are  found  fragments  of  schist,  which  indicate 
that  the  syenite  is  eruptive  later  than  the  schists.  At  Winchell  lake 
the  syenite  upon  the  top  grades  down  by  an  apparent  transition  into 
