LAKE   SUPERIOR   REGION.  363 
later  considered  it  to  probably  underlie  the  fossiliferous  red  sand- 
stone of  St.  Marys  River.  It  was  placed  by  Jackson,  Marcou,  and  for 
a  long  time  by  Bell,  as  the  "  New  Red  sandstone."  Very  early  others, 
including  Dawson  (Sir  William),  Foster,  Houghton,  Logan,  Owen, 
Whitney,  and  Rogers,  regarded  the  sandstone  as  "  Lower  Silurian  " 
or  Potsdam.  In  1873  Rominger  finally  demonstrated  what  Hough- 
ton had  long  before  stated,  that  the  horizontal  sandstone  is  directly 
overlain  by  the  "  Calciferous  "  formation.  The  sandstone  was  there- 
fore placed  as  Potsdam,  which  position  it  has  held  since  that  time 
without  dispute  by  anyone  acquainted  with  the  region. 
It  was  very  early  seen  that  the  horizontal  sandstone  is  newer  than 
the  granites  and  slates  of  Lake  Superior,  which  occupy  a  lower  posi- 
tion than  the  Keweenawan.  Schoolcraft  saw,  as  early  as  1821,  the 
unconformity  between  the  granite  and  the  sandstone  at  Granite  Point, 
and  between  the  latter  and  the  slates  on  St.  Louis  River  at  the  head 
of  Lake  Superior.  Bayfield  recognized  this  unconformity  in  1829, 
saying  that  the  many  instances  of  the  conjunction  of  the  sandstone 
and  the  granite  proved  that  the  sandstone  was  deposited  after  the 
granite  occupied  its  present  position.  Rogers  saw  the  same  relations 
between  the  sandstone  and  the  slates  of  Chocolate  and  Carp  rivers, 
although  at  first  he  regarded  the  latter  as  "  Primal."  Owen,  in  1847, 
described  like  unconformable  relations  between  the  horizontal  sand- 
stone referred  to  the  Potsdam  and  the  crystalline  rocks  in  northern 
Wisconsin.  Norwood,  in  1847,  again  saw  the  unconformity  between 
the  Lake  Superior  sandstone  and  the  slates  of  St.  Louis  River  at 
Fond  du  Lac,  described  by  Schoolcraft  many  years  before.  Foster, 
in  1848,  saw  the  same  unconformable  relations  between  the  sandstones 
and  the  slates  at  L'Anse.  Since  these  early  discoveries  of  the  rela- 
tions between  the  sandstone  and  the  crystalline  rocks  were  announced 
they  have  been  confirmed  at  these  original  localities  and  at  numerous 
other  localities  by  many  observers. 
As  to  the  relations  of  the  Lake  Superior  sandstone  with  the  sand- 
stones interstratified  with  the  trappean  rocks,  i.  e.,  the  Keweenawan, 
there  has  been  the  greatest  diversity  of  opinion,  and  the  question  is 
one  on  which  there  is  not  yet  entire  unanimity,  although  the  weight 
of  the  evidence  is  so  strongly  in  favor  of  the  inferior  position  of 
the  Keweenawan  series  that  this  conclusion  is  rejected  by  but  few 
geologists. 
Bayfield,  Bigsby,  Burt,  Rogers,  Schoolcraft,  and  Whittlesey  made 
no  distinction  between  the  Lake  Superior  and  Keweenawan  sand- 
stones, apparently  not  recognizing  that  there  was  any  question  of 
their  not  being  equivalent.  Jackson,  followed  by  Bell,  for  many 
years  apparently  regarded  the  Keweenawan  sandstones  as  later  than 
the  Lake  Superior  sandstone.  Jackson  places  the  former  as  "  New 
Red  "  and  states  that  the  sandstone  of  the  Pictured  Rocks  may  not  be 
