158  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
evidence  is  so  strongly  in  favor  of  the  inferior  position  of  the  Kewee- 
naw series  that  this  conclusion  is  doubted  by  bnt  few  geologists. 
Bayfield,  Bigsby,  Burt,  Rogers,  Schoolcraft,  and  Whittlesey  made 
no  distinction  between  the  lake  Superior  and  Keweenawan  sandstones, 
apparently  not  recognizing  that  there  was  any  question  of  their  not 
being  equivalent.  Jackson,  followed  by  Bell,  for  many  years  appar- 
ently regarded  the  Keweenawan  sandstones  as  later  than  the  lake  Su- 
perior sandstone.  Jackson  places  the  former  as  New  Red,  and  states 
that  the  sandstone  of  the  Pictured  rocks  may  not  be  of  the  same  age. 
Bell  at  first  thought  the  Keweenawan  Permian  or  Triassic,  while  cog-i 
nizant  of  the  fact  that  the  lake  Superior  sandstone  is  older  than  the 
Triassic,  but  recently  this  writer  places  the  sandstone  as  probably  uil 
conformably  above  the  Keweenawan.  Foster,  Wads  worth,  Whitueyjj 
and  Winchell  (N.  H.),  after  comparisons  and  studies  of  the  problem,  havd 
maintained  that  the  lake  Superior  and  Keweenawan  sandstones  belong 
to  the  same  series.  Agassiz,  Brooks,  Chamberlin,  Dawson,  Houghton^ 
Irving,  Logan,  Macfarlane,  Bell,  Owen,  Pumpelly,  Rominger,  Selwyn^ 
Strong,  Sweet,  and  Wooster  have  held  as  their  latest  view  that  the 
Keweenaw  series  is  older  than  the  lake  Superior  sandstone.  Agassiz 
at  first  regarded  all  the  sandstones  of  the  same  age,  but  came  to  the 
conclusion  afterwards  that  the  sandstone  was  deposited  against  the  up- 
turned Keweenaw  series.  Agassiz,  Brooks,  Chamberlin,  Dawson,  Irj 
ving,  Owen,  Pumpelly,  Rominger,  Strong,  Sweet,  and  Wooster  maintain 
a  great  unconformity  between  the  two.  Macfarlane  held  that  there  was 
a  doubtful  unconformity  between  the  Keweenaw  series  and  the  lake 
Superior  sandstone,  the  former  occupying  an  inferior  position.  Hough- 
ton's,  Logan's,  and  Selwyn's  position  is  that  the  Keweenaw  series  is  a 
downward  extension  of  the  lake  Superior  red  sandstone.  The  latter  is 
regarded  by  Logan  as  probably  Ohazy,  and  the  Keweenawan  therefore 
Oalciferous  or  Potsdam.  Selwyn  and  Bell  now  place  the  Keweenawan 
as  Cambrian. 
The  relations  of  the  horizontal  sandstone  in  northern  Wisconsin  to 
the  melaphyres  and  traps  regarded  as  Keweenawan  have  been  de: 
scribed  by  all  observers  to  be  those  of  unconformity,  the  horizontal 
sandstone  resting  upon  the  upturned  edges  of  the  Keweenaw  series. 
The  only  point  of  difference  has  been  whether  this  sandstone  is  Potsdam 
or  not.  It  is  so  regarded  by  the  Wisconsin  geologists  and  by  Owenj 
but  is  by  N.  H.  Winchell  called  St.  Croix  and  is  placed  above  the  Pots? 
dam.  The  true  position  of  this  sandstone  another  will  discuss,  but  no 
one  doubts  that  it  belongs  near  the  base  of  the  Northwestern  Paleozoics^ 
The  extensive  area  of  horizontal  sandstone  about  Agogebic  lake  be- 
tween the  two  highly  tilted  trap  ranges  was  long  ago  cited  by  Brooks 
and  Pumpelly  as  evidence  that  the  lake  Superior  sandstone  is  far  latel 
in  age,  it  being  found  not  distant  from  the  highly  tilted  Keweenawan 
eruptives. 
The  controversy  has  been  most  extended  as  to  the  relations  of  the 
