284  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.        [bull.  260. 
The  west-northwest  faults  have  approximately  the  same  general 
strike  as  the  lead-silver  lodes  and  were  produced  by  the  same  or  simi- 
lar stresses.  That  some  of  the  faults  were  formed  prior  to  the 
deposition  of  the  ore  is  fairly  certain. 
In  addition  to  the  west-northwest  faults  there  are  several  disloca- 
tions of  nearly  north-south  trend,  which  attain  their  greatest  struc- 
t  ura]  importance  in  the  central  part  of  the  district.  The  most  promi- 
nent member  of  this  group  is  the  Dobson  Pass  fault,  which  has  been 
traced  from  a  point  about  3  miles  north  of  Wallace  to  within  2  miles 
1  of  Eagle,  The  fault  dips  to  the  west  at  an  angle  of  35°  or  less, 
and  is  normal.  At  Dobson  Pass,  5  miles  north  of  Murray,  the 
fault  has  dropped  the  Striped  Peak  formation  against  the  Prichard 
slate,  indicating  a  throw  of  at  least  6,000  feet. 
Another  great  dislocation  of  this  group  is  the  Carpenter  Gulch 
fault,  which  has  been  followed  from  the  northern  boundarv  of  the 
district  southward,  past  the  mouths  of  Prichard  and  Beaver  creeks,  ] 
for  12  miles  to  a  point  about  3  miles  northwest  of  Wallace.     Its  I 
course  is  irregular  and  it  dips  west  and  southwest  at  a  moderate  J 
angle.    This  fault  is  an  overthrust  of  approximately  1,000  feet. 
Slaty  cleavage,  usually  of  a  rather  irregular  character,  is  a  well-J 
marked  structural  feature  of  the  finer-grained  rocks  of  the  Coeurj 
d'Alene  region,  and  a  distinct  fissility  has  in  some  places  been  pro- J 
duced  in  moderately  coarse  quartzites.  It  is  best  developed  in  the  I 
Prichard  slate  and  in  the  lower  part  of  the  Wallace  formation.  This! 
cleavage  is  usually  independent  of  bedding,  and  shows  a  marked] 
tendency  to  conform  in  strike  to  the  general  trend  of  the  longer  folds* 
and  in  both  strike  and  dip  to  the  major  faults.  Local  zones  of  slaty  J 
cleavage  are  the  usual  accompaniments  of  the  lead-silver  lodes  ofm 
Mullan  and  Canyon  Creek.  In  no  case  does  this  structure  attain  the! 
perfection  found  in  roofing  slate.  The  cleavage  surfaces  intersect! 
at  small  angles,  and  the  rocks  split  somewhat  irregularly  into  len-1 
ticular  flakes.  The  dip  of  the  cleavage  nearly  everywhere  ranges 
from  south  westward  to  southward  or  westward. 
Age  of  deformation. — Lindgren a  has  shown  that  the  granitic 
(quartz-monzonite)  batholith  of  the  Clearwater  and  BitterrootH 
mountains  is  probably  of  post-Triassic  age.  That  intrusion  was! 
undoubtedly  associated  with  orogenic  uplift.  We  know  that  thel' 
erosion  which  exposed  this  granite  and  reduced  it  and  the  surround-j 
ing  rocks  to  a  region  of  subdued  relief  must  have  been  later  than] 
the  intrusion.  We  know  further  that  the  whole  central  Idaho  region] 
must  have  been  again  uplifted,  this  time  as  a  plateau,  in  pre-Miocenel 
time,  for  the  Coeur  d'Alene  River  in  its  lower  course  had  cut  below 
its  present    bed   before  the  eruption   of  the   Columbia    River   basalt 
a  Loc.  cit.,  p.  20. 
Ip 
