IRON  AND  MANGANESE. 
THE  LAKE  SUPERIOR  IRON  REGION  DURING  1903. 
By  C.  K.  Leith. 
VERMILION    DISTRICT. 
The  Vermilion  district  of  Minnesota  is  described  in  Monograph 
XLV,  by  J.  Morgan  Clements.  It  is  accompanied  by  both  general 
and  detail  maps  of  the  range  between  Tower  and  (iunnint  Lake.  The 
field  work  for  this  report  was  done  by  Messrs.  Clements,  Van  Hise, 
Bayley,  Merriam,  and  Leith.  The  features  of  the  monograph  were 
summarized  in  Bulletin  No.  213. 
MENOMINEE    DISTRICT. 
The  Menominee  district  is  described  by  W.  S.  Bayley  in  Monograph 
XL VI.  This  is  a  volume  of  501  pages,  accompanied  by  a  general  map 
of  the  Menominee  range,  and  several  detail  maps.  The  discussion  of 
the  geologic  features  does  not  differ  essentially  from  that  in  a  prelim- 
inary report  on  the  district  published  in  1900  as  the  Menominee  Special 
geologic  folio  (No.  (>2),  but  in  the  present  discussion  much  of  interest 
has  been  added,  including  a  complete  description  of  the  ores,  their 
geologic  occurrence,  structure,  physical  characteristics,  chemical  com- 
position, mineralogical  composition,  etc. 
The  ores  are  confined  to  the  Vulcan  formation  of  the  so-called  Upper 
Huronian  series.  The  Vulcan  formation  is  subdivided  into  three  mem- 
bers, from  the  base  up,  the  iron-bearing  Traders  member,  the  Brier 
slate,  and  the  iron- bearing  Curry  member.  The  ores  are  further  con- 
lined  to  the  Traders  and  Curry  members,  and,  other  things  being  equal, 
are  more  likely  to  occur  at  lower  and  higher  horizons  than  at  the 
middle  horizon. 
The  richer  ores  are  found  in  situations  where  the  attitudes  of  the  rocks  are  such 
as  to  furnish  converging  channels  for  percolating  waters,  and  the  largest  deposits 
are  in  the  main  channels  toward  which  the  drainage  converges.  Consequently,  the 
deposits  of  large  size  rest  upon  relatively  impervious  foundations,  which  are  in  such 
positions  as  to  constitute  pitching  troughs.     A  pitching  trough  may  be  made  (a)  by 
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