THE   CORDILLERAS.  851 
been  found.  On  the  west  these  sediments  extend  to  Coeur  d'Alene 
Lake,  where  they  are  probably  faulted  down  against  the  granitic  and 
gneissic  rocks  forming  the  western  shore  of  that  picturesque  body  of 
water.  On  the  north  practically  nothing  is  known  of  the  extent  of 
these  Algonkian  rocks.  It  is  not  unlikely  that  they  continue  north- 
ward past  Pend  Oreille  Lake  and  are  connected  with  the  great  series 
of  Algonkian  beds  known  to  occur  in  the  northwest  corner  of  Mon- 
tana. On  the  east,  beds  of  the  same  character  as  those  occurring  in 
the  Coeur  d'Alene  district  extend  to  Missoula  River  at  the  mouth  of 
the  St.  Regis  de  Borgia.  Here  there  is  apparently  some  change  in 
lithological  character,  but  quartzites  and  red  and  green  siliceous 
argillites,  probably  of  Algonkian  age,  extend  at  least  to  the  town  of 
Missoula,  in  Montana,  and  probably  for  some  distance  farther  east. 
The  area  of  Algonkian  sediments  has  a  width  of  about  80  miles  be- 
tween Coeur  d'Alene  Lake  and  Missoula  River,  and  it  is  probable 
that  extensive  exposures  of  Algonkian  beds  continue  100  or  more 
miles  to  the  eastward,  connecting  the  Coeur  d'Alene  area  with  the 
known  Algonkian  areas  of  central  and  northern  Montana. 
On  the  south  Lindgren a  has  shown  that  the  sedimentary  rocks 
near  Lolo  Pass,  which  are  probably  part  of  the  same  series  that  pre- 
vails in  the  Coeur  d'Alene  Mountains,  are  cut  off  by  the  great  granitic 
batholith  of  central  Idaho. 
Lindgren,135  in  1905,  states  that  identified  pre-Cambrian  rocks  are 
absent  in  central  Idaho  and  eastern  Oregon.  There  are,  however, 
several  smaller  areas  of  coarse  gneisses  inclosed  in  much  later  and 
probably  late  Mesozoic  granites  and  quartz  monzonites,  which  occupy 
so  much  space  in  these  States.  These  areas  are  rarely  directly  con- 
nected with  distinct  sediments.  It  is  belieA^ed  that  they  represent 
part  of  an  old  Archean  basement.  One  of  these  areas,  about  10  miles 
square,  occurs  some  20  miles  northwest  of  Sumpter,  Oreg.  Another 
similar  mass  occurs  90  miles  southeast  of  Lewiston,  Idaho.  This  is 
about  30  miles  long  and  20  miles  wide.  Other  gneissoid  masses  are 
inclosed  in  granite  on  the  Nez  Perce  trail  near  the  boundary  of  Idaho 
and  Montana.  One  of  these  areas  connects  with  a  mass  of  sediments 
of  unknown,  possibly  pre-Cambrian,  age.  These  same  sediments  ap- 
pear in  patches  along  the  Bitterroot  Range,  and  are  finally  developed 
on  a  great  scale  in  northern  Idaho  between  Lolo  Fork  and  the  North- 
ern Pacific  Railway.  Xo  fossils  have  ever  been  found  in  them  and 
they  are  suspected  to  be  of  the  same  age  as  the  Belt  series  of  central 
Montana. 
Collier,130  in  1906,  in  discussing  the  ore  deposits  in  the  St.  Joe 
River  basin,  Idaho,  states  that  the  Algonkian  sedimentary  series  of 
"Lindgren,  Waldemar,  A  geological  reconnaissance  across  the  Bitterrool  Range  and 
Clearwater  Mountains  in  Montana  and  Idaho:  Prof.  Paper  U.  S,  Geol.  Survey  No.  27, 
1904,  p.  16. 
