878  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
Another  area  of  Shuswap  rocks,  separated  from  the  first  by  a  band 
of  limestones,  occurs  on  Omenica  River  above  the  Oslinca,  The  band 
has  a  width  of  10  miles. 
The  Shuswap  series  is  overlain  by  Lower  Paleozoic  strata. 
Dawson,188  in  1901,  describes  the  geology  of  the  Rocky  Mountain 
region  in  Canada.  The  oldest  rocks  of  the  region  belong  to  the 
Shuswap  series,  of  Archean  a  age.  The  Shuswap  series  characterizes 
considerable  areas  of  the  Selkirk,  Columbia,  and  adjacent  ranges 
in  the  southern  part  of  British  Columbia.  It  is  known  also  in  the 
Cariboo  Mountains  and  near  the  sources  of  the  North  Thompson 
and  Fraser,  about  latitude  53°.  It  is  again  well  developed  on  Finlay 
River,  where  the  country  has  been  geologically  examined,  between 
the  parallels  of  latitude  5G  and  57.  Northward  to  this  point  these 
rocks  appear  to  be  confined  to  a  belt  lying  west  of  the  Lar amide 
Range  and  to  come  to  the  surface  seldom,  if  at  all,  in  that  range. 
Farther  north  similar  rocks  h  occur  in  the  Yukon  district  in  several 
ranges  lying  more  to  the  west,  but  still  with  nearly  identical  charac- 
ters, in  so  far  as  they  are  known.  The  Shuswap  series  includes 
highly  metamorphosed  sediments  with  perhaps  the  addition,  of  con- 
temporaneous bedded  volcanic  materials.  They  are  grayish  mica 
gneisses,  with  some  garnetiferous  and  hornblendic  gneisses,  glitter- 
ing mica  schists,  crystalline  limestones,  and  quartzites.  Gneisses  in 
association  with  the  last-mentioned  rocks  often  become  highly  cal- 
careous or  siliceous  and  contain  scales  of  graphite,  which  are  also 
often  present  in  the  limestones.  These  bedded  materials  are,  how- 
ever, associated  with  a  much  greater  volume  of  mica  schists  and 
gneisses  of  more  massive  appearance,  most  of  which  are  evidently 
foliated  plutonic  rocks,  and  are  often  found  to  pass  into  unfoliated 
granites.  The  association  of  these  different  classes  of  rocks  is  so 
close  that  it  may  never  be  possible  to  separate  them  on  the  map  over 
any  considerable  area.  The  granites  may  often  have  been  truly 
eruptive  in  origin,  but  the  frequent  recurrence  of  quartzites  among 
them  in  some  regions  indicates  that  they  are,  at  least  in  part,  the 
result  of  a  further  alteration  of  the  bedded  rocks.  The  original 
bedded  portions  of  the  series  closely  resemble  those  of  the  Grenville 
series  of  the  Province  of  Quebec,  and  the  associated  gneisses  resemble 
the  Fundamental  gneiss  of  the  same  region.  The  greatest  thickness 
of  the  Shuswap  rocks  so  far  measured,  where  there  is  no  suspicion 
of  repetition,  on  Kootenai  Lake,  is  about  5,000  feet,  but  even  here 
there  are  doubtless  included  considerable  intercalations  of  foliated 
eruptives. 
To  the  Cambrian  are  assigned  McConnells  Bow  River  series,  the 
Nisconlith  series  of  the  Selkirk  region  to  the  west,  and  the  Adams 
a  Pre-Cambrian.  6  Probably  Paleozoic. — Authors. 
