858  PRE-CAMBRTA  a    GEOLOGY   OF    NORTH    AMERICA. 
origin.  They  are,  in  part  at  least,  of  igneous  origin,  and  none  of 
them  show  any  traces  of  sedimentary  origin.  Their  relations  to  the 
Algonkian  rocks  are  those  of  unconformity.  The  Algonkian  rocks 
are  found  in  the  mountain  tracts  of  the  Little  Belt  Range,  in  Castle 
Mountain,  and  in  the  low  range  crossed  by  Sixteenmile  Creek  in  the 
southwest  corner  of  the  Little  Belt  Mountains  quadrangle.  They  are 
divided  into  the  Neihart  quartzite  and  the  Belt  formation,0  both  of 
which  are  parts  of  what  Walcott  has  called  the  Belt  terrane. 
The  Neihart  quartzite  is  a  hard  pink  and  gray  quartzite  forming 
the  base  of  the  Belt  terrane  for  this  area.  It  is  found  in  the  vicinity 
of  Neihart,  in  the  Little  Belt  Mountains.  Its  thickness  is  about  600 
feet.  The  Belt  formation  consists  mainly  of  slaty  siliceous  shales, 
but  also  contains  interbedded  limestone  and  quartzite.  Fossils  found 
in  this  series  (in  the  shales  above  the  formation  which  Walcott  has 
named  the  Newland  limestone  member  of  the  Belt  terrane)  represent 
the  earliest  forms  of  life  }^et  known.  Near  Neihart  the  Algonkian 
period  is  represented  by  4,000  feet  of  beds,  while  farther  south  and 
west  the  thickness  is  much  greater. 
Overlying  the  Algonkian  rocks  conformably  are  rocks  containing 
Middle  Cambrian  fossils.  North  of  Neihart  they  rest  directly  on  the 
Archean. 
Weed,148  in  1901,  describes  and  maps  the  geology  of  the  Elkhorn 
mining  district  of  Montana.  Doubtfully  referred  to  the  Algonkian 
are  the  Turnley  hornstones.  The  lower  division  is  200  feet  thick  and 
consists  of  shale  metamorphosed  to  a  very  dense  hornstone  com- 
posed of  light-brown  biotite  and  quartz.  A  bed  of  impure  iron  ore 
20  to  30  feet  thick  occurs  in  the  middle  lower  part  of  the  formation. 
The  quartzitic  hornstones  overlie  the  basal  beds  just  noted  and  are 
200  feet  thick.  The  rocks,  though  well  bedded,  are  very  dense  and 
hard  and  are  of  a  gray-black  color,  so  that  they  closely  resemble  the 
andesites.  In  color,  composition,  and  relation  to  the  overlying 
quartzite  the  rocks  correspond  to  the  red  Spokane  shale  of  the  Belt 
terrane  seen  at  Whitehall,  20  miles  south,  at  Townsend  to  the  east, 
and  at  Helena  on  the  north. 
Willis,149  in  1902,  describes  and  maps  the  stratigraphy  and  struc- 
ture of  the  Lewis  and  Livingston  ranges  of  the  Front  Range  of  the 
northern  Rocky  Mountains  of  Montana  and  Alberta.  The  Lewis  and 
Livingston  ranges  consist  of  stratified  rocks  of  Algonkian  age,  as 
determined  on  fossils  which  were  found  by  Weller  in  the  lowest  lime- 
stone of  the  series  and  identified  by  Walcott  as  probably  being  Beltina 
danai,  the  species  of  crustacean  discovered  in  the  Greyson  shales  of 
the  Belt  Mountains.  The  Algonkian  series  consists  of  limestone, 
argillite,  and  quartzite,  classified  in  six  formations  and  aggregating 
a  The  Belt  formation  includes  the  various  lithological  members  of  the  Belt  terrane 
which  Walcott  has  named  the  Ohamberlin  shale,  the  Newland  limestone,  the  Greyson 
shale,  the  Spokane  shale,  and  the  Empire  shale. 
