CHAPTER  III. 
LAKE    SUPERIOR    REGION. 
SECTION  1.    MICHIGAN. 
SUMMARY  OF  LITERATURE. 
Houghton,1  a  in  1840,  divides  the  rocks  in  the  south  and  southeastern 
part  of  the  Upper  Peninsula  into  Primary  and  sedimentary.  The 
Primary  region  stretches  continuously  in  a  northwestward  direction 
for  many  hundreds  of  miles,  skirting  portions  of  the  shores  of  Lake 
Superior,  and  constituting  the  highlands  between  that  lake  and  the 
Lake  of  the  Woods.  From  these  highlands  it  stretches  a  little  east  of 
Lake  Winnipeg  far  to  the  northwest,  finally  constituting  the  im- 
mense "  barren  grounds  "  of  the  British  Possessions.  The  rocks  of 
St.  Marys  River  and  adjacent  region  comprise  greenstone,  argillite, 
and  granular  quartz  rock,  which  passes  into  an  almost  conglomeratic 
quartz  rock.  In  this  occur  small  quantities  of  hematitic  iron  ore. 
The  sedimentary  rocks  include  the  Lake  Superior  sandstone  and  lime 
rock  and  shales.  The  Lake  Superior  sandstone  is  nearly  continuous 
on  the  southern  shore  of  Lake  Superior,  and  in  its  easterly  prolonga- 
tion rests  against  and  upon  the  Primary  range  of  St.  Marys  River, 
where  it  passes  conformably  below  the  limestone  above.  The  Lake 
Superior  sandstone,  in  its  easterly  prolongation,  does  not  attain  a 
very  great  thickness,  but  in  proceeding  westerly  this  thickness  is 
vastly  increased,  attaining  on  the  south  shore  of  Lake  Superior  to 
several  hundred  feet.  A  careful  search  for  fossils  in  this  sandstone 
has  failed  to  reveal  a  single  one. 
Houghton,2  in  1841,  divides  the  older  rocks  of  the  Upper  Penin- 
sula of  Michigan  into  (1)  Primary,  (2)  trap,  (3)  metamorphic,  (4) 
conglomerate,  (5)  mixed  conglomerate  and  sandstone,  (6)  lower  or 
red  sandstones  and  shales,  and  (7)  upper  or  gray  sandstone.  The 
Primary  rocks  are  in  a  broad  sense  granite.  The  granitic  rocks  are 
largely  traversed  by  greenstone  dikes.  The  trap  rocks  of  the  district 
in  a  chronological  order  would  follow  the  metamorphic  slates  and 
quartz  rocks,  but  the  granitic  rocks  pass  by  almost  insensible  grada- 
tion into  the  greenstones  of  the  trap  formation. 
The  sedimentary  rocks  on  the  south  and  southeast  of  the  main  trap 
range  are  scarcely  disturbed,  while  those  on  the  north  and  northwest- 
"  For  notes  see  end  of  chapter,  p.  386. 
108 
