106  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
duo  to  faulting  along  the  contact,  or  are  due  to  the  losing  of  the  vein 
fracture  in  porphyry  which  had  become  decomposed  and  softened 
previous  to  the  period  of  Assuring. 
Conglomerate. — A  few  small  patches  of  conglomerate  were 
observed.  The  rock  consists  usually  of  coarse,  well-rounded  peb- 
bles and  cobblestones  of  gneiss,  granite,  pegmatite,  and  quartz,  up  t( 
one  fool  in  diameter,  embedded  in  a  well-indurated  matrix  resembling 
arkose  sandstone.  The  rock  is  so  well  consolidated  that  when  brokeii 
the  fractures  often  pass  through  instead  of  around  the  pebbles.  Tw< 
outcrops  occur  midway  up  the  southeast  slope  of  Lincoln  Mountain 
Conglomerate-like  rocks  are  found  to  the  north  of  Empire  at  a  lowe 
level,  and  also  on  the  top  of  Leavenworth  Mountain.  It  has  not  beei 
possible  so  far  to  correlate  the  different  patches  of  conglomerate  o 
to  determine  definitely  their  origin.  Perhaps  they  are  in  part  at  leas 
stream  deposits  of  late  Tertiary  or  Quaternary  age,  formed  at  variou 
stages  of  the  down  cutting  of  the  region. 
Pleistocene  deposits. — Glacial  deposits  of  at  least  two  differer! 
epochs  are  found  in  certain  parts  of  the  region  up  to  elevations  c 
1,500  feet  or  more  above  the  valleys.  Ground,  lateral,  and  termini 
moraines  occur  in  the  district;  glacially  striated  and  grooved  roc 
surfaces  are  also  numerous.  Terraces  and  alluvial  flats  occasional] 
occur  as  a  result  of  the  damming  of  the  streams  by  morainic  materia 
or  by  debris  from  landslides. 
Faulting. — Numerous  minor  faults  are  known  to  intersect  the  rod 
of  the  district.     It  is,  however,  almost  impossible  to  follow   faul 
on  the  surface,  as  the  pre-Cambrian  rocks  form  a  "  complex,"  ai 
the   surface   is   weathered   and    frequently  covered  with  debris.     II 
tracing  out  one  of  the  porphyry  dikes  above   Silver  Plume,  Ikjs 
ever,  two  faults  involving  an  offset  on  the  surface  of  about  200  fe 
(  ach   were  encountered.     Most  of  the  more  intimate   knowledge 
the   faulting  is  derived  from  the  underground   workings  of  mini 
Here   small   faults   are   frequently   encountered.      In   the   cases   de 
nitely  determined  the  displacement  is  only  from  a  few  inches  to 
or  '20  feet;  but  it  is  probable  that  in  some  instances  it  has  been  inn 
greater.     Most  of  the  veins  have  formed  along  fault  planes,  and  the 
has  often  been  subsequent  or  post-mineral  movement,  both  along  t 
vein  /ones  and  transverse  to  them.    Around  Silver  Plume  and  Georfj 
town  the  dip  of  movement  striae  on  slickensided  fault  surfaces  a 
rule  does  not  exceed  20°  from  the  horizontal.     Instances  of  dips 
to  35°  or  40°  are  rare.       Around  Empire,  however,  clips  of  from  A 
to  75°  are  much  more  common  than  the  more  nearly  horizontal  on  i 
Contacts  between  two  rock  formations  of  unequal  resistance,  si 
as  granite  and  gneiss,  or  some  other  older  rock  and   porphyry,  In' 
evidently  been  especially  favorable  to  faulting.     The  porphyry  <li 
