874  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
Mountain,  another  in  the  Salmon  Mountains,  both  subordinate  parts 
of  the  Klamath  Mountains  in  California,  and  a  third,  somewhat 
doubtful,  at  the  northern  end  of  the  Klamath  Mountains  on  Rogue 
River  in  Oregon.  The  two  lines  of  outcrop  at  their  southern  ends 
are  about  40  miles  apart  and  approximately  parallel,  running  north- 
west-southeast. The  first  belt  runs  northwest  from  the  Sacramento 
Valley  through  the  Yallabally  and  South  Fork  mountains  to  the  sea, 
a  distance  of  more  than  100  miles,  with  an  average  width  of  somewhat 
more  than  5  miles.  The  prevailing  rock  is  a  gray  or  greenish-gray, 
more  or  less  silky  mica  schist  in  which  the  mica  is  sericite.  Although 
in  well-defined  folia  and  fibers,  giving  the  mass  a  decided  schistose 
structure,  the  mica  is  not  well  crystallized  in  distinct  scales.  The 
quartz  is  generally  in  excess  of  the  mica,  and  the  mass  is  locally  full 
of  quartz  veins.  Along  the  western  border  of  this  belt  in  places  is  a 
greenish,  more  or  less  schistose,  rock  whose  relations  are  not  clearly 
understood.  It  is  composed  chiefly  of  quartz  and  epidote,  as  if  a 
product  of  contact  metamorphism.  The  long  narrow  belt  of  mica 
schist  of  South  Fork  Mountain  is  bounded  on  the  southwest  by  unal- 
tered sandstones,  shales,  and  conglomerates  of  Mesozoic,  in  part 
Cretaceous,  age,  but  on  the  northeast,  the  direction  in  which  the  crum- 
pled schistose  structure  generally  dips,  it  is  limited  by  a  broad  belt  of 
Devonian  sediments  mingled  in  a  very  perplexing  fashion  with  an 
extensive  body  of  plutonic  and  volcanic  rocks. 
The  second  or  Salmon  Mountain  belt  is  somewhat  less  regular,  ex- 
tending from  Bully  Choop  Mountain  northwest  by  Weaverville  into 
the  Salmon  Mountains,  where  it  appears  to  turn  northeasterly  toward 
Yreka.  The  mica  schist  a  of  this  belt,  occasionally  containing  thin 
limestones,  is  associated  with  hornblende  schist,6  which  in  the  vicinity 
of  Weaverville  and  Bully  Choop  appears  to  be  for  the  most  part  a 
metamorphosed  igneous  rock,  but  in  certain  localities  Hershey  finds 
evidence  of  its  derivation  from  sediments  overlying  the.  mica  schist, 
with  a  total  thickness  for  both  schists  of  3,500  feet. 
The  third  schist  area  of  the  Klamath  Mountains  is  in  Oregon,  ex- 
tending north  beyond  Rogue  River  into  the  Port  Or  ford  region, 
where  it  has  been  definitely  mapped  c  as  the  Colebrook  formation. 
The  principal  rock  is  sericite  schist,  associated  with  phyllites  and 
beds  which  are  clearly  fragmental,  of  sedimentary  origin.  These 
rocks  lie  unconformably  beneath  the  Knoxville  beds,  and  while  it  is 
certain  only  that  they  were  metamorphosed  in  pre-Cretaceous  time,  it 
is  possible  that  they  are  of  the  same  age  as  the  schists  of  California 
toward  which  the  exposure  extends,  at  least  as  far  south  as  Smith 
River. 
°  Abrams  mica  schist  of  Hershey,  op.  cit,  p.  226. 
b  Salmon  hornblende  schist  of  Hershey,  op.  cit.,  p.  228. 
*  Geologic  Atlas  U.  S.,  Port  Orford  folio   (No.  89),  1903. 
