ISOLATED   AULAS    IN    MISSISSIPPI    VALLEY.  741 
phyries,  and  porphyritic  breccias.  Ila worth  describes  gradations 
between  the  granite  and  the  porphyritic  rocks.  At  Pilot  Knob  and 
in  the  adjacent  area  are  found  water-deposited  rocks  which  comprise 
porphyry  conglomerates,  fine-grained  beds  of  the  same  character,  and 
well-bedded  iron  ores  and  ferruginous  slates.  The  porphyry  sedi- 
ments and  the  iron-bearing  rocks  are  interbedded  in  such  a  way  as  to 
suggest  a  deposition  under  water  of  nonfragmental  iron-formation 
material  similar  to  that  in  the  Lake  Superior  region,  this  deposition 
being  interrupted  by  the  accumulation  of  volcanic  material  which 
itself  was  to  a  considerable  extent  worked  over  by  water.  The  iron 
ores  and  associated  ferruginous  slates  have  all  the  aspects  of  Lake 
Superior  ores  derived  from  the  alteration  of  original  bedded  iron 
carbonate  or  ferrous  silicate  formations.  Iron  ores  found  at  Iron 
Mountain  occur  largely  as  great  irregular  masses  and  veins  in  the 
porphyry  and  ma}^  be  of  different  origin.  The  relations  of  the  sedi- 
mentary rocks  to  the  massive  granites  and  porphyries  are  not  known. 
The  unaltered  horizontal  Paleozoic  rocks  rest  on  the  deeply  eroded 
crystalline  rocks,  the  conglomerates  adjacent  to  Pilot  Knob  and  Iron 
Mountain  containing  numerous  bowlders  of  iron  ore. 
There  is,  then,  in  southeastern  Missouri  a  pre-Cambrian  clastic 
series  associated  with  igneous  rocks  which  may  be  either  older  or 
younger.  The  rocks  show  resemblances  to  both  Archean  and  Algon- 
kian  rocks  of  the  Lake  Superior  country,  and  there  is  no  way  to 
separate  them.    They  are  accordingly  mapped  as  pre-Cambrian. 
SECTION  5.     OKLAHOMA. 
SUMMARY   OF  LITERATURE. 
Hill,73  in  1891,  finds  in  Indian  Territory,  in  the  heart  of  the  area 
occupied  by  the  Chickasaw  Nation,  a  granite  called  the  Tishomingo 
granite,  which  appears  to  be  of  pre-Paleozoic  age. 
Bain,74  in  1900,  describes  the  geology  of  the  Wichita  Mountains  of 
Oklahoma.  Gabbros  and  porphyries  of  pre-Cambrian  and  probably 
of  Archean  age  are  present.  The  gabbro  is  more  prominent  in  the 
western  portion  of  the  mountains,  being  especially  well  developed  m 
the  Raggedy  Mountains,  and  the  porphyry  is  more  common  in  the 
eastern  pari  of  the  mountains,  being  typically  developed  at  Carroll- 
ton  Mountain. 
Taff,75  in  1904,  describes  and  maps  the  geology  of  the  Arbuckle 
and  Wichita  mountains,  in  Indian  Territory  and  Oklahoma.  In  the 
Arbuckle  mountains,  southwestern  Indian  Territory,  unconformably 
below  middle  Cambrian  sediments,  are  granite,  granite  porphyry. 
and  aporhyolite  containing  basic  dikes.  Tli  granite  (Tishomingo) 
occurs  in  the  eastern  part  of  the  mountains  in  a  rudely  triangular 
area  -JO  miles  in  length  and  10  miles  wide  in  its  widest  part,  near  the 
