84  PRE-CAMBRIAN    ROOKS    OF    NORTH    AMERICA.  [bull.  86. 
• 
deposits  and  the  metamdrphic  uplifts.  There  are  cases  where  the  trap, 
instead  of  being  forced  across  the  stratification,  has  spread  out  between 
the  beds,  forming  alternate  strata  of  trap  and  sandstone  without  any 
visible  conglomerate. 
Shumard,80  in  1852,  mentions  the  quartzite  ranges  of  Sauk  county, 
near  Baraboo.  The  quartzites  are  surmounted  by  sandstone,  and  all 
are  included  in  the  great  sandstone  formation  of  southern  Wisconsin. 
Jackson,81  in  1853,  maintains  that  the  red  and  gray  sandstones  of 
lake  Superior  are  above  the  rocks  of  Devonian  age.  They  rest  horizon- 
tally around  Silurian  limestone,  which  has  an  inclination  on  Sturgeon 
river  near  Keweenaw  point  of  30°.  In  point  of  fact  the  sandstones  of 
lake  Superior  are  the  exact  equivalents  of  those  of  Nova  Scotia,  where 
trap  rocks  of  the  same  age  as  those  of  lake  Superior  pass  through  them. 
The  amygdaloidal  trap  of  Keweenaw  point  and  isle  Koyale  is  a  vesicu- 
lar rock  formed  by  the  interfusion  of  sandstone  and  trap  rock. 
Marcou,82  in  1853,  after  having  made  a  complete  tour  of  lake  Supe 
rior,  places  the  red  sandstone  and  traps  bearing  copper  as  the  new  red 
sandstone,  and  correlates  it  with  the  new  red  sandstones  of  Nova 
Scotia,  New  Brunswick,  Connecticut,  New  Jersey,  Maryland,  and  Vir- 
ginia. 
Whitney,83  in  1854,  states  that  the  basin  of  lake  Superior  is  a  great 
synclinal  trough  caused  by  a  depression  of  the  sandstone,  which  appears 
to  form  its  bed.  The  northern  and  eastern  shores  for  much  of  their  dis- 
tances are  faced  by  perpendicular  cliffs,  while  the  southern  shore  is 
comparatively  low.  The  reason  for  this  difference  is  that  on  the  east 
and  north  the  sandstone  which  originally  existed  there  has  been  worm 
away  and  the  more  enduring  granitic  and  trappean  rocks  only  are  left 
The  age  and  relations  of  the  sandstones  of  lake  Superior  to  the  trap- 
pean rocks  and  Azoic  slates  are  again  described  as  before. 
Schoolcraft,84  in  1855,  states  that  the  granitic  strata  of  the  Thou- 
sand isles  reappear  on  the  north  shore  of  lakes  Huron  and  Superior, 
underlie  the  bed  of  the  latter,  and  are  found  on  the  rough  coast  between- 
Chocolate  river  and  Keweenaw,  and  cross  the  Mississippi  near  the  falffl 
of  St.  Anthony.  The  straits  of  St.  Mary's  appears  to  be  the  ancient 
line  of  junction  between  the  great  calcareous  and  granitic  series  oh 
rocks  on  the  continent.  The  island  of  St.  Joseph  is  chiefly  primitive 
rocks  and  at  its  south  end  is  largely  loaded  with  granitic,  porphyritic  and 
quartzitic  bowlders.  The  north  shore  of  the  river,  opposite  the  island^ 
is  entirely  of  the  granitic  series,  which  continues  to  Gros  cap  on  lakq 
Superior.  The  red  sandrock  of  lake  Superior  is  regarded  as  the  Old 
Red  sandstone.  The  formation  of  red  jasper  in  white  quartz  exists  on 
the  southern  foot  of  Sugar  island.  In  the  granitic  conglomerates  are 
seen  red  feldspathic  granite,  black  shining  hornblende  rock,  white  fatty 
quartz,  and  striped  jasper,  all  held  together  firmly.  Volcanic  action 
appears  to  have  thrown  up  the  trap  rocks  of  the  Pic,  of  the  Porcupine, 
chain,  of  isle  Poyale,  and  the  long  peninsula  of  Keweenaw.     The  sand- 
