LAKE    SUPERIOR   REGION. 
175 
Wright,94  in  1905,  reports  on  progress  in  the  mapping  of  the 
Keweenawan  rocks  of  the  Porcupine  Mountain  region  of  Michigan 
by  the  Michigan  Geological  Survey.  A  number  of  faults  in  the 
Keweenawan  are  described,  most  of  them  contemporaneous  or  subse- 
quent to  the  deposition  of  the  copper.  Important  changes  in  the 
mapping  of  this  district,  said  to  be  necessary,  are  not  described. 
Lane,05  in  1907,  gives  an  outline  account  of  the  geology  of  Kewee- 
nawan Point,  with  special  reference  to  the  geological  relations  of  the 
copper  deposits.  No  essential  modifications  of  the  earlier  writers 
are  reported. 
Lane  and  Seaman,90  in  1907,  present  a  geological  section  of  Michi- 
gan, the  lower  part  of  which  is  as  follows: 
Partial  geological  section  of  Michigan. 
Sys- 
tem. 
Series. 
Formation. 
Thickness 
(feet). 
Character  of  rocks. 
ej 
St.  Peter 
0-75 
Sandstone;     white,   water  bearing,   in 
hollows  of  Calciferous  dolomite,  but 
absent  often. 
o 
Calciferous 
255-180 
Buff  and  bluish  dolomites,  often  sandy, 
o 
with  dolomitic  white  sandstones. 
Munising 
200 
Sandstone;   white  or  light,  water  bear- 
Neo-C  arabria  n 
Jacobs  ville 
0-1,500+ 
Sandstone;   red  and  brown  and  striped 
(Saratoga  n; 
a> 
redstone. 
(4,000?) 
with  streaks  of  red  clay  shale,  con- 
Potsdam;   Up- 
Z   i 
glomeratic  where  it  laps  upon  older 
per  Keweenaw- 
formations. 
an,  perhaps). 
M 
Hiatus." 
(900+)? 
Sandstone;    red,  with  some  felsitic  and 
basic  debris,  and  salt  water. 
Mio-Cambrian. 
No 
350-600 
Shales;    dark,  fissile  beds,  with  dark 
basic  fragments,  and  products  of  de- 
composition of  lavas;  copper  bearing. 
Outer 
1,000-3,500 
Conglomerate;    very  heavy,  red,  with 
m 
o 
large  rounded  bowlders  of  all  lower 
£i 
formations,   including  jaspilitic  iron 
o 
o3 
ores, agate  amygdules,  gabbro,  aplites, 
>— <    < 
etc. 
Ph 
Lake  Shore . . . 
1,800-400 
Traps;   basaltic  lavas,  and  at  least  one 
a, 
o 
(the  "Middle")  conglomerate. 
c 
Great 
2, 200-340 
Conglomerate;     very   heavy,   like   the 
a 
u 
Outer  conglomerate. 
•2 
Eagle  River 
2,300-1,417 
Group  of  basic  lava  flows,  with  frequent 
,0 
beds  of  sediment,  Marvine's  c. 
■     6 
A  si 
1,456-2,400+ 
(.">()  sediment) 
Group  of  basic  lavas  of  the  "ashbed" 
a 
type  with  scoriaceous  sediment  and 
Keweenawan 
onlv  50  feet  or  so  of  conglomerate. 
(Lower  Kewee- 
Locally felsites. 
nawan,  perhaps 
Central  Mine 
3,823-25,000? 
Group;    mainly  of  lavas  of  the  augitic 
Eo-Cambrian). 
(480  sediment) 
ophite  type,  with  infrequent  sedi- 
ments. At  the  top  is  the  "Mesnard 
epidote,"  and  just  beneath  it  the  heav- 
iest flow,  oyer  1 ,000  feet  thick  at  times, 
known  as  the  Greenstone.  Under 
this  is  the  Allouez  conglomerate. 
Marvine's  No.  15.  No.  13  is  the  Calu- 
met and  Beela  conglomerate  or  lode. 
The  Kearsarge  lode  is  shortly  above  9. 
Bohemian  Range. 
(?)-9,500+ 
(500  sediment  1 
Group;  mainly  of  basic  lavas  but  with 
intrusive  and  effusive  felsites  and 
coarse  labradorite  porphyrites;  aiso 
intrusive  diabase  dikes  and  gabbro 
and  gabbro  aplites. 
o  The  relation  of  the  Freda  to  the  Lake  Superior  sandstone  is  uncertain; 
formation. 
probably  they  are  one 
