sckbl.]         [BON    AND    MANGANESE    OBES    OF    CTNITED   STATES.  319 
(1)  The  Lake  Superior  ore-,  which  consist  chiefly  of  hematites, 
lave  been  studied  and  mapped  in  great  detail  by  the  Survey.  A 
lumber  of  monographs,  by  Prof.  C.  R.  Van  Hise  and  hi-  assistants, 
lave  been  issued,  each  publication  taking  up  one  of  the  districts  or 
4  ore  ranges."  The  concluding  monograph  of  this  series,  which  i-  to 
summarize  the  geology  of  the  cut  ire  lake  region,  is  now  being  pre- 
>ared  by  Professor  Van  Hise.  The  series,  taken  a-  a  whole  i-  prob- 
ably the  most  complete  discussion  of  any  group  of  ore  deposits  ever 
Published.  Incidentally  the  studies  in  this  district  have  led  to 
inportant  generalization.-  in  regard  to  the  formation  of  ore  deposits 
n  general. 
(-_!)  The  Clinton  ore-,  which  outcrop  almost  continuously  from 
-entral  New  York  to  Alabama,  occur  a-  beds  of  oolitic  red  hematite 
ri  the  Clinton  group  of  the  Silurian.  At  present  they  an-  exploited 
xtensively  only  in  the  southern  pari  of  their  range,  in  Tennessee, 
reorgia,  and  Alabama.  Much  of  tie-  area  in  which  they  occur  has 
)een  mapped  by  tin-  Survey,  and  the  results  published  in  geologic 
olios  No-.  2,  1.  6,  v.  L9,  20,  25,  33,  35,  7:».  and  78;  the  locations  of  the 
reas  described  in  the  folio-  are  given  in  the  tables  on  pages  1  1  to  17. 
The  commercial  importance  of  these  Clinton  ores  in  the  southern 
Appalachians  renders  advisable  a  detailed  economic  survey  of  their 
ceurrence  and  relation-hip-.  During  the  season  of  L905  further 
Fork  in  the  Clinton  ore-  ha-  therefore  been  planned  by  the  Survey. 
'ooperation  in  this  work  has  been  arranged  with  the  Alabama  Geo- 
pgical  Survey,  the  investigation  being  placed  in  charge  of  the  writer. 
l  detailed  survey  of  the  important  Birmingham  district,  conducted 
n  a  cooperative  basis,  is  already  under  way.  During  L904  new  devel- 
.pinent-  in  the  ore  region  at  the  extreme  southern  end  of  this  district 
rere  investigated  by  Survey  parties,  and  a  brief  reporl  on  these 
ccurrences  i-  presented  by  Mr.  Burchard. 
Aside  from  their  direel  commercial  importance,  the  Clinton  ores 
resent  problems  of  greal  interest  to  the  economic  geologist.  [Jnlike 
io-t  other  ore-,  they  appear  to  have  been  formed  simultaneously  with 
ie  strata   in   which   they  are   inclosed.     The  geographic  conditions 
hieh  favored  tin-  deposition,  and  the  chemical  processes  by  which  it 
fas  brought  about  can  not  he  fully  stated  without  considerable 
etailed  study  in  addition  to  the  fact-  now  on  :-<<-i>i<\.  It  is  hoped 
nit  the  investigations  on  the  eastern  iron  ores,  now  in  progress,  will 
irow  light  on  these  questions. 
(3)  The  ore-  of  the  Appalachian  Valley  are  limonites  (brown 
lematites),  mostly  associated  with  the  great  series  of  Carnbro- 
prdovician  lime-tone-  which  form  the  floor  of  this  valley  from  Ver- 
jont  to  Alabama.  These  ore-  have  been  mapped  in  a  number  of 
pologic  folio-,  while  a  discussion  of  an   important   Georgia  district 
ill  he  found  in  Bulletin  213,  L.  S.  Geological  Survey,  pages  233-242. 
