864  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
Here  the  banded  gneissoid  granite,  cut  by  granitic  and  basic  rocks, 
has  a  foliation  in  the  same  direction  for  many  miles.  Associated 
with  the  gneisses  along  and  near  Cherry  Creek  on  the  west  side  of 
the  Madison  River  is  an  area  8  miles  long  and  4  miles  wide,  which 
consists  of  crystalline  limestones,  mica  schists,  quartz  schists,  and 
gneisses,  very  highly  inclined.  This  is  called  the  Cherry  Creek 
"  series."  So  far  as  seen,  the  structure  of  the  series  is  conformable 
with  the  lamination  of  the  gneiss  and  granite.  The  apparent  con- 
formity of  the  Cherry  Creek  series  and  the  gneisses  may  in  future  be 
explained  by  any  one  of  three  hypotheses — obliterated  unconformity, 
downward  metamorphism,  or  intrusion  of  the  gneissic  series.  The 
truncated  edges  of  all  the  above  are  traversed  by  the  little-disturbed 
Cambrian. 
Besides  the  Cherry  Creek  group  there  is  a  pre-Cambrian  clastic 
series  called  the  Belt  series,  ranging  up  to  10,000  or  12,000,  or 
possibly  even  30,000,  feet  in  thickness,  resting  upon  the  Archean 
unconformabry.  This  series  is  exposed  along  East  Gallatin  River, 
in  the  canyon  of  Jefferson  River,  in  Bridger  Canyon,  in  the  Little 
Belt  Mountains,  northwesterly  past  Helena  into  British  Columbia, 
and  westward  beyond  the  state  boundary  into  Idaho.  (See  PL  I.) 
In  general,  fine-grained  rocks,  including  limestones,  shales,  and  sand- 
stones, predominate  to  the  southeast  in  the  Belt  Mountains,  in  the 
Rocky  Mountain  front,  and  westward  to  Idaho.  Coarse  conglom- 
erates, grits,  and  sandstones  predominate  to  the  northwest,  especially 
to  the  west  of  the  Kootenai  Valley,  which  region  must  have  been 
the  great  source  of  the  sediments.  The  Belt  series  is  correlated  by 
Walcott  with  most  of  Dawson's  Adams  Lake  (Selkirk)  group  and 
all  of  his  Nisconlith  group.  Middle  Cambrian  sediments  overlie  the 
Belt  series  unconformabry  for  all  the  area  except  the  Lewis  Range 
and  the  Cceur  d'Alene  and  Kootenai  districts.  The  Bow  River  group 
seems  to  be  lower  Cambrian  and  is  taken  by  Walcott  to  represent, 
in  part  at  least,  the  erosion  interval  between  the  Belt  series  and  the 
lower  Cambrian.  The  Belt  series  contains  sparse  fossils  of  probable 
pre- Cambrian  age. 
While  the  Cherry  Creek  group  is  not  anywhere  in  contact  with  the 
Belt  series,  its  extreme  metamorphism  and  its  common  structure  with 
the  gneisses  make  it  highly  probable  that  it  is  unconformable  below 
the  Belt  series,  since  the  latter  rests  upon  the  truncated  edges  of  the 
gneisses. 
Occupying  a  position  similar  to  that  of  the  Belt  series  are  great 
series  of  sedimentary  rocks  in  the  Uinta  Mountains,  in  the  Wasatch 
Mountains,  and  in  British  Columbia.  These  in  all  probability  are 
contemporaneous  with  the  Belt  series,  and  together  mark  a  continu- 
ous area  of  deposition,  and  therefore  a  geological  province,  in  early 
Cambrian  or  late  Algonkian  time.    It  may  be  that  the  area  should  be 
