THE   CORDTLLERAS.  887 
"  Rapid  "  schist,  and  its  green  facies  may  be  an  altered  intrusive.  The 
"Lake  quartzite  schist,"  the  next  younger  formation,  is  apparently 
essentially  a  mica  schist,  and  mineralogically  does  not  differ  from  the 
two  older  formations  except  in  the  presence  of  graphite.  It  appears 
that  these  three  formations  are  lithologically  very  similar,  and,  as 
their  relations  are  so  much  in  doubt,  that  they  might  well  be  grouped 
together.  They  seem  to  form  a  broad  belt  of  highly  metamorphosed 
sediments  with  some  intrusives,  which  on  the  north  are  succeeded  by 
heavily  bedded  crystalline  limestone  and  mica  schists,  termed  the 
Bettles  "  series."  The  field  distribution  indicated  on  Schrader's  map 
suggests  that  the  schist  scries  and  the  limestones  are  unconformable. 
Schrader's0  second  journey,  during  which  he  crossed  the  Rocky 
Mountains  to  the  north,  yielded  far  more  definite  results,  though  he 
was  unable  to  correlate  them  with  those  of  his  previous  season. 
The  Ska  jit  formation  he  puts  at  the  base  of  the  succession,  describ- 
ing it  as  made  up  of  heavily  bedded  crystalline  limestones  and  mica 
-chist s.  Some  obscure  organic  remains  indicate  that  the  Skajit  is 
probably  not  older  than  the  "  Upper  Silurian." 
A  group  of  mica  schists  and  quartz  mica  which  forms  an  east-west 
belt  south  of  the  Skajit  formation  has  been  called  by  Schrader  the 
Totsen  "series,"  and  is  regarded  by  him  as  younger  than  the  Skajit 
formation,  but  to  the  writer  the  evidence  would  seem  stronger  that 
they  were  older  and,  in  fact,  the  equivalent  of  the  "Rapids"  and 
"Lake"  formations  to  the  east.  If  this  is  the  case,  the  Skajit  can  be 
correlated  with  the  Bettles.  A  comparison  of  the  two  parallel  sec- 
tions, one  on  the  upper  Chandalar  and  the  other  on  John  River, 
shows  in  both  instances  mica  schist  and  quartz-mica  schist  and  green- 
stone or  amphibolite  schist  on  the  south,  and  heavily  bedded  white 
crystalline  limestone  with  some  mica  schist  on  the  north.  If  the 
writer's  interpretation  is  correct  the  correlation  of  Schrader's  pre- 
Devonian  terranes  would  be  as  follows: 
("  Upper  Silurian")  Skajit  formation=Bettles  "series." 
Totsen  "scries"  and  greenstone  schist^"  Rapids,"  "Lake," 
and  amphibolite  schists. 
It  is  of  importance  to  note  that  this  succession  bears  a  close  resem- 
blance to  that  in  the  oldest  sediments  of  the  Yukon-Tanana  region 
already  described.  The  older  horizon,  made  up  as  it  is  of  mica  and 
quartz  schist,  is  similar  to  the  Birch  Creek  schist,  while  the  younger, 
consisting  of  crystalline  limestones  and  mica  schists,  bears  a  resem- 
blance to  the  Fortymile  group. 
The  close  similarity  between  the  succession  south  and  that  north  of 
the  Yukon  suggests  the  identity  of  the   Fortymile  group  with  the 
"  Schrader,  F.  C,  A  reconnaissance  in  northern  Alaska,  etc.  :  Prof.  Paper  U.  S,  Geol. 
Survey    No.    20,    1904,    pp.   55   62. 
