166  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  88. 
imity  to  the  volcanic  forces,  and  while  the  great  masses  of  granite-gneiss 
are  below  the  dioritic  group,  these  rocks  are  also  interstratified  with 
and  cut  the  dioritic  rocks,  the  whole  granitic  group  being  regarded  as 
of  igneous  origin,  and  later  in  age  than  the  sedimentaries.  The  likeness 
of  the  dioritic  group  and  Lawson's  Keewatin  at  once  suggests  itself. 
As  has  been  seen,  Eoniinger's  later  studies  led  hirn  materially  to  modify 
his  opinions  and  to  bring  them  more  nearly  in  harmony  with  the  con- 
elusions  of  Brooks  and  Irving. 
N.  H.  WinchelPs  succession  is:  Keweenawan,  Animikie,  Noriaii, 
Pewabic  quartzite  (all  of  which  are  included  in  the  Taconic),  Keewatin, 
Vermilion,  Laurentian  (which  are  included  in  the  Archean  or  Azoic). 
The  Keweenawan  is  doubtfully  called  Potsdam,  and  is,  with  the  Ani- 
mikie, placed  as  the  Georgia  formation;  and  the  Pewabic  quartzite  is 
provisionally  placed  with  the  Potsdam  granular  quartz.  Included  in  the 
Taconic  are  the  quartzites  of  Minnesota,  Iowa,  Dakota  and  Wisconsin. 
The  part  of  the  succession  placed  in  the  Taconic  differs  from  living's  suc- 
cession for  this  part  of  the  column  in  that  the  formations  which  Winchell 
includes  in  the  Norian  and  Pewabic  are  regarded  as  the  great  basal  gab- 
bro  mass  of  the  Keweenawan,  between  the  upper  Keweenawan  and  the< 
Animikie  instead  of  beloAv  the  Animikie.  It  is  not  neeessary  to  say 
that  Irving  regarded  all  of  these  members  as  pre-Cambrian.  The  sue) 
cession  within  the  Archean  is  the  same  as  that  of  Lawson,  the  difference 
being  only  that  Yermilion  is  substituted  for  Coutchiching.  Also  the 
Keewatin  elastics,  Vermilion  schists,  and  Laurentian  gneiss  are  regarded 
as  in  complete  conformity,  all  detrital,  and  the  lower  members  but  more 
metamorphosed  than  the  upper. 
Alexander  WinchelPs  succession  below  the  Keweenawan  is  Huronian, 
Keewatin,  Vermilion  and  Laurentian.  At  the  base  of  the  Huronian  is 
a  great  structural  break.  The  three  lower  series  are  in  conformity  and 
grade  into  each  other.  This  is  much  the  same  as  this  part  of  the  suc- 
cession given  by  1ST.  H.  Winchell,  exeept  that  one  great  series,  thei 
Ogishki  conglomerate,  is  placed  by  the  latter  as  a  part  of  the  Animikie 
(Huronian)  while  by  Alexander  Winchell  it  is  placed  with  the  Keewatin. 
Doubtless  to  the  minds  of  many  the  great  thickness  of  the  combined 
Keewatin  and  Coutchiching  of  Profs.  Winchells  and  Lawson  will  be 
presumptive  evidence  against  the  structure  which  they  have  worked 
out.  This  thickness  as  given  by  Alexander  Winchell  is  more  than 
30,000  feet,  while  Lawson  gives  the  Keewatin  a  thickness  of  5  miles  and 
the  Coutchiching  a  thickness  of  4  or  5  miles,  or  in  the  neighborhood  of 
50,000  feet.  The  manner  in  which  the  structure  of  the  Keewatin  and 
Coutchiching  schists  always  strike  parallel  to  and  encircle  the  adjacent 
granite  masses  suggests  that  these  intrusives  have  developed  slaty 
cleavage  or  schistose  structure  which  has  been  mistaken  for  bedding. 
Lawson  supposes  the  intruding  granite  has  upthrust  the  beds  until 
they  now  stand  on  end.  That  both  schistose  structure  and  bedding, 
with  marked  discordance  to  each  other,  exist  east  of  Rainy  lake  is  posi- 
tively maintained  by  Pumpelly  and  Smyth. 
