van  ins,;.]  LAKE    SUPERIOR    REGION.  159 
two  series  on  Keweenaw  point.  A  part  of  what  lias  been  regarded  as 
the  lake  Superior  sandstone,  adjacent  to  the  trap  range,  has  been  shown 
by  Wadsworth  to  belong  with  the  Keweenaw  series,  and  it  is  even  yet 
a  debatable  question  as  to  just  where  at  certain  places  the  lake  Superior 
sandstone  begins  and  the  Keweenaw  series  ends;  because  by  all  it  is 
now  agreed  that  near  this  contact  is  an  ancient  fault  of  great  magni- 
tude, along  which  post-Potsdam  slipping  has  taken  place. 
In  considering  the  question  whether  the  lake  Superior  sandstone  is  a 
part  of  the  Keweenawan,  the  general  held  relations  are  more  significant 
than  all  else.  Wherever  the  Keweenaw  series  appears  in  its  character- 
istic development  about  lake  Superior,  from  Michipicoten  on  the  east 
to  Duluth  on  the  west,  from  Thunder  bay  on  the  north  to  Keweenaw 
point  on  the  south,  it  is  a  titled  series,  the  inclinations  rarely  being  less 
than  30°,  never  less  on  the  south  shore,  while  more  commonly  they  are 
much  higher,  running  often  to  80°.  The  lake  Superior  sandstone,  on 
the  other  hand,  wherever  found,  is  horizontal,  except  along  lines  of  con- 
tact with  Keweenawan  or  other  rocks,  and  here  the  tilting  has  been 
explained  to  be  due  to  faulting.  The  only  locality  remote  from  a  con- 
tact at  which  the  sandstone  is  said  not  to  be  horizontal  is  Traverse 
island,  and  at  this  place  the  facts  upon  which  the  statement  is  based 
have  not  been  published.  The  lake  Superior  sandstone  runs  as  a  long 
tongue  for  a  distance  of  more  than  50  miles,  always  in  horizontal  atti- 
tude, gradually  narrowing  to  the  west;  between  the  north  and  south 
highly  inclined  Keweenawan  trap  ranges  to  near  the  Montreal  river. 
Nowhere  is  it  interlaminated  with  or  cut  by  a  single  eruptive  rock  of 
any  kind.  The  finding  of  detrital  rocks  between  the  lava  flows  of  the 
South  range  of  the  Keweenawan  has  no  bearing  against  this  assertion 
any  more  than  does  the  existence  of  such  rocks  in  the  main  trap  range. 
Before  it  can  be  concluded  that  such  tilted  interlaminated  detritals  are 
a  part  of  the  horizontal  Eastern  sandstone  the  two  must  be  traced 
together  in  continuous  exposure. 
These  broad  field  relations  and  the  absence  of  trap  point  with  irre- 
sistible force  to  the  conclusion  that  the  lake  Superior  sandstone  is  a  far 
ater  formation,  laid  down  since  the  Keweenawan  was  deposited,  uptilted, 
md  eroded.  If  this  is  not  the  case,  that  it  in  broad  areas  should  have 
wholly  escaped  the  dynamic  movements  which  upturned  the  Keweenaw 
series  everywhere  about  lake  Superior  is  absolutely  inexplieable. 
Equally  strange  is  the  fact  that  it  has  everywhere  escaped  intrusive 
material.  It  is  not  a  common  thing  for  eruptive  activity  which  extends 
3ver  distances  of  300  miles  east  and  west  and  100  miles  north  and  south 
to  continue  in  full  force  up  to  and  stop  along  a  ruled  line  100  miles 
long.  That  this  occurred  must  be  believed  if  the  lake  Superior  sand- 
stone is  regarded  as  belonging  to  that  part  of  the  Keweenaw  series, 
nterbedded  with  the  traps,  as  advocated  by  Wadsworth.  The  absence 
if  eruptive  material  in  the  horizontal  sandstone  on  the  theory  that  it  is 
i  part  of  the  Keweenawan  can  be  explained  only  by  regarding  it  as  the 
