rax.some.1  COEUR    d'aLENE    DISTRICT,  IDAHO.  277 
though  steep  and  high,  rising  in  places  over  3,500  feet  above  the 
nearest  trunk  streams,  are  comparatively  smooth  of  slope  and  not  par- 
ticularly rugged  of  crest.  This  general  plateau-like  character  is  not 
a  local  feature  peculiar  to  the  Coeur  d'Alene  Mountains,  but  is  con- 
tinuous on  the  south,  with  the  great  dissected  plateau  forming  the 
western  slope  of  the  Bitterroot  Mountains  and  the  Clearwater  Moun- 
tains.'1 
The  district,  with  the  exception  of  a  small  part  along  the  eastern 
border,  which  is  drained  by  the  St.  Regis  de  Borgia  and  other  tribu- 
taries of  Clark  Fork,  drains  westward  through  the  Coeur  d'Alene 
River  into  the  lake  of  the  same  name.  The  South  Fork,  which  rises 
a  few  miles  east  of  Mullan,  is  a  comparatively  feeble  stream,  over- 
burdened in  summer  with  the  tailings  from  the  concentrating  mills. 
Its  principal  tributaries  within  the  area  considered  are  Canyon,  Nine- 
mile,  and  Placer  creeks,  which  enter  at  Wallace,  and  Big  Creek,  which 
debouches  from  the  south  between  Osburn  and  Kellogg. 
The  North  Fork,  which  rises  north  of  the  district  and  flows  out  of 
its  northwest  corner,  is  a  beautiful  clear  stream,  navigable  for  light 
boats  for  many  miles  above  Kingston,  on  the  Oregon  Railway  and 
Navigation  Company's  line,  where  it  is  joined  by  the  South  Fork. 
Its  principal  tributaries  within  the  district  are  Prichard  and  Beaver 
creeks,  both  of  which  enter  it  from  the  south. 
Nearly  all  the  streams  of  the  district  flow  in  deep  V -shaped  valleys, 
but  the  larger  streams,  such  as  the  North  and  South  forks  and  Prich- 
ird  and  Beaver  creeks,  have  partially  filled  or  aggraded  their  valleys — 
a  feature  which  is  characteristic  of  all  the  streams  flowing  into  Coeur 
d'Alene  Lake,  and  which  becomes  more  noticeable  nearer  their  mouths. 
GENERAL  GEOLOGY. 
General  character  and  distribution  of  the  rocks. — The  prevailing 
ocks  of  the  Coeur  d'Alene  Mountains  are  arenaceous  and  argilla- 
eous  sediments  of  great  thickness.  They  constitute  an  apparently 
pnformable  series,  of  which  neither  the  stratigraphic  base  nor  top 
ippears  in  the  district  nor,  so  far  as  known,  in  the  surrounding 
egion.  No  fossils  have  been  found  in  them,  and  they  are  probably 
f  Algonkian  age. 
On  the  west  these  sediments  extend  to  Coeur  d'Alene  Lake, 
vhere  they  are  probably  faulted  down  against  the  granitic  and 
rneissic  rocks  forming  the  western  shore  of  that  picturesque  body  of 
vater.  On  the  north  practically  nothing  is  known  of  the  extent  of 
hese  Algonkian  rocks.  It  is  not  unlikely  that  thev  continue  north- 
yard   past   Pend   Oreille   Lake   and    are   connected    with    the   great 
ries  of  Algjonkian  beds  known  to  occur  in  the  northwestern  corner 
"  Lindgren,  W.,  loc.  cit.,  p.  14. 
