850  PRE-CAMBRTAN    GEOLOGY    OF    NORTH    AMERICA. 
is  apparently  overlain  to  the  east  by  more  than  20,000  feet  of  sedi- 
mentary rocks  described  by  Dalya  and  probably  in  part  the  equiva- 
lent of  the  Algonkian  sediments  of  the  Coeur  d'Alene  district.6 
The  granitoid  gneiss  forms  a  belt  at  least  10  miles  wide  along  the 
international  boundary,  and  seems  to  be  continuous  with  a  broad  band 
of  gneiss  and  granite  stretching  from  Bonners  Ferry  on  the  east  to 
Priest  Lake  on  the  west  and  extending  southward  past  Pend  Oreille 
and  Coeur  d'Alene  lakes.  Some  crystalline  schist  is  associated  with 
the  gneiss  along  Boundary  Creek,  west  of  Porthill,  the  gneiss  being 
intrusive  into  the  schist.  Near  the  head  of  Priest  River,  in  the  ex- 
treme northwest  corner  of  the  State,  crystalline  schists  predominate 
over  the  gneiss.  They  include  mica  schist,  quartz  schist,  limestone 
schist,  and  schistose  conglomerates,  with  some  massive  quartzite. 
No  fossils  have  been  found  in  these  metamorphosed  sediments. 
Their  reference  to  the  Algonkian  depends  upon  the  fact  that  they 
belong  to  a  crystalline  complex  that  as  a  whole  underlies  the  unmeta- 
morphosed  sediments  east  of  the  Kootenai  River,  the  latter  being 
probably  pre-Cambrian. 
Lindgrex,133  in  1904,  made  a  geological  reconnaissance  across  the 
Bitterroot  Range  and  Clearwater  Mountains,  in  Montana  and  Idaho. 
Practically  the  entire  area  of  the  Bitterroot  and  Clearwater  moun- 
tains is  occupied  b}7  granite  with  some  gneiss.  West  of  the  Clear- 
water River,  and  only  imperfectly  exposed  below  the  lava,  is  an  ex- 
tensive sedimentary  area  adjoining  this  granite;  smaller  sedimentary 
areas  are  exposed  on  Lolo  Fork  and  on  the  head  of  the  South  Fork 
of  Bitterroot  River.  In  no  place  have  well-defined  fossils  been  found, 
but  there  is  some  foundation  for  the  belief  that  the  two  last-named 
areas  on  the  east  side  are  very  old,  possibly  pre-Cambrian,  while  the 
western  area  probably  includes  Triassic,  Carboniferous,  and  possibly 
still  older  sediments.  The  granite  constitutes  a  great  batholith  whose 
age  is  not  certain,  but  probably  post-Triassic.  The  gneisses  include 
older  gneisses  of  the  Clearwater  Mountains,  probably  of  pre-Cam- 
brian age,  and  later  gneisses  resulting  from  the  deformation  of  the 
granite  occurring  principally  on  the  eastern  side  of  the  Bitterroot 
Mountains.  On  the  accompanying  map  all  are  colored  together  as 
pre-Tertiary. 
Ransome,134  in  1905,  describes  the  geology  of  the  Cceur  d'Alene  dis- 
trict of  Idaho.  The  prevailing  rocks  are  Algonkian  sediments,  at 
least  10,000  feet  thick,  consisting  of  arenaceous  and  argillaceous  ma- 
terials. No  fossils  have  been  found  in  them.  Neither  the  strati- 
graphic  base  nor  top  in  this  district  or  in  the  surrounding  region  has 
a  Daly,  R.  A.,  Secondary  origin  of  certain  granites  :  Am.  Jour.  Sci.,  4th  ser.,  vol.  20, 
1905,  pp.  186-187. 
b  Ransome,  F.  L.,  Ore  deposits  of  the  Coeur  d'Alene  district,  Idaho  :  Bull.  U.  S.  Geol, 
Survey  No,  260,  1905,  pp.  277-282, 
