736  PRE-CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA. 
metamorphic  limestone  is  one  member  of  the  porphyry  series,  but  it 
is  now,  by  physical  and  chemical  agents,  greatly  changed  from  its 
original  condition  and  is  very  manganiferous.  Another  member  of 
this  same  succession  is  a  porphyry  conglomerate  or  breccia,  consisting 
of  pebbles  of  red  and  compact  porphyry  containing  grains  of  quartz 
and  crystals  of  feldspar  and  cemented  by  porphyry  of  a  similar  char- 
acter. This  rock  resembles  the  Calumet-Hecla  conglomerate  of  Lake 
Superior. 
Schmidt,58  in  1873,  also  describes  the  iron-ore  deposits  of  Iron 
Mountain,  Pilot  Knob,  Shepherd  Mountain,  Cedar  Hill,  Buford  Hill, 
Big  Bogg  Mountain,  Lewis  Mountain,  Cuthbertson  Bank,  and  Hogan 
Mountain.  The  succession  at  Cedar  Hill  includes  slates  of  red-banded 
porphyry,  stratified  quartz  porphyry,  slates  of  red  porphyry,  green 
porphyry,  banded  jasper,  and  jasper  with  specular  ore. 
Shumard,59  in  1873,  states  that  granite  is  found  in  Laclede,  Craw- 
ford, and  Ste.  Genevieve  counties. 
Broadhead  and  Norwood,00  in  1874,  describe  granite  and  porphyry 
at  numerous  points  in  Madison  County.  On  the  west  side  of  St. 
Francis  Kiver,  in  the  NW.  i  NE.  ±  sec.  33,  T.  34  N.,  E,  5  E.,  there  is 
an  exposure  of  sandstone  and  conglomerate  resting  directly  on  the 
granite. 
Haworth,61  in  1888,  states  that  the  Archean  area  of  Missouri  covers 
an  irregularly  outlined  portion  of  no  less  than  ten  different  counties 
and  extends  to  the  west  as  far  as  Texas  County,  to  the  north  and 
northeast  as  far  as  Washington,  St.  Francois,  and  Ste.  Genevieve 
counties;  to  the  east  it  passes  through  Madison  County,  and  to  the 
south  nearly  through  Wayne  County;  but  only  a  small  portion  of 
this  territory  is  covered  by  Archean  rocks.  The  rocks  are  the  differ- 
ent kinds  of  porphyry,  which  predominate,  granite,  and  dikes  of 
diabase  and  diabase  porphyry.  Numerous  instances  were  observed 
where  the  stratified  rocks  overlie  the  massive  ones  and  are  noncon- 
formable  with  them.  Nowhere  at  the  contact  zone  was  metamor- 
phosed limestone  or  sandstone  observed.  The  granites,  so  far  as 
observed,  occur  on  low  ground,  while  the  hills  are  almost  invariably 
composed  of  porphyry.  At  numerous  places  dikes  of  various  sizes 
occur,  sometimes  in  the  granite  and  sometimes  in  the  porphyry  and, 
as  stated  by  Broadhead,  sometimes  in  the  sandstone.  Detailed 
descriptions  are  given  of  the  granites,  porphyries,  and  dike  rocks. 
Pumpelly  and  Van  Hise,62  in  1890,  find  that  at  Iron  Mountain 
the  ore  (specular  hematite),  in  its  original  position,  occurs  in  the 
form  of  veins  in  the  porphyry.  These  veins  are  sometimes  of  very 
considerable  thickness,  running  as  high  as  30  feet.  They  vary  from 
this  size  to  those  much  smaller,  ramifying  through  and  cutting  the 
porphyry  in  various  directions.  In  some  places  on  the  mound  be- 
tween the  stratified  sandstone  and  the  porphyry  is  a  pre-Silurian, 
