884  PRE-CAMBRIAN    GEOLOGY   OF   NORTH   AMERICA. 
sive  in  the  sedimentary  series,  and  this  is  borne  out  by  the  latest 
studies  of  Prindle  in  the  Yukon-Tanana  region.  On  the  earlier  recon- 
naissance maps a  of  the  Yukon-Tanana  region  extensive  areas  of 
Archean  gneisses  and  basal  granites  are  indicated.  The  later  and 
more  detailed  studies  of  this  field  by  Prindle 6  have  shown  these  maps 
to  be  at  fault,  for  it  appears  that  the  gneisses  in  this  belt  are  chiefly 
altered  igneous  rocks  intruded  in  the  sediments. 
In  the  course  of  an  exploration  c  in  the  Mount  McKinley  region 
the  writer  crossed  a  belt  of  gneisses  south  of  the  Tanana  near  the 
head  of  the  Cantwell,  but  there  was  no  opportunity  for  detailed 
studies.  The  typical  rock  of  this  area  is  a  coarse  augen  gneiss  iden- 
tical with  that  found  in  the  gneissic  complex  of  the  upper  Tanana. 
These  rocks  appear  to  be  altered  eruptives,  associated  with  Paleozoic 
sediments. 
A  small  area  of  gneissoid  granites  and  some  mica  schists  in  the 
lower  Chandalar  River  basin  north  of  the  Yukon  were  assigned  by 
SchraderrZ  to  a  basement  complex.  The  evidence  presented  by  him 
indicates  that  they  may  equally  well  be  sheared  intrusives,  and  hence 
they  are  not  here  included  with  the  Archean. 
Gneisses  are  also  reported  by  Spurr6  in  the  Kuiu  Mountains  east 
of  the  lower  Yukon,  and  Collier  f  observed  gneissoid  rocks  occurring 
west  of  the  Yukon,  near  the  mouth  of  Melozi  River.  Both  of  these, 
in  a  general  way,  lie  in  the  extension  of  the  gneissic  belts  already 
described  and  are  here  included  in  the  metamorphic  terranes. 
On  the  first  geological  map  of  any  part  of  Alaska,  published  over 
half  a  century  ago,  Grewingk^  indicated  a  belt  of  gneissic  rocks 
extending  along  the  backbone  of  the  Alaska  Peninsula.  These  he 
assigned  to  the  "  Primitive  "  rocks.  Spurr  h  describes  this  as  a  pre- 
Jurassic  basal  granite.  The  recent  work  of  Martin  l  goes  to  show 
that  this  is  probably  an  igneous  complex  which  was  intruded  during 
early  Mesozoic  time. 
°  Spurr,  J.  E.,  The  geology  of  the  Yukon  gold  district :  Eighteenth  Ann.  Rept.  U.  S. 
Geol.  Survey,  pt.  3,  1898,  PI.  XXXVIII,  p.  252.  Brooks,  Alfred  EL,  A  reconnaissance  in 
the  Tanana  and  White  river  basins  :  Twentieth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  7, 
1900,  map  24,  p.  460.  Brooks,  Alfred  EL,  A  reconnaissance  from  Pyramid  Harbor  to 
Eagle  City  :  Twenty-first  Ann.  Rept.  TJ.  S.  Geol.  Survey,  pt.  2,  1900,  PL  XLVII,  p.  356. 
b  L.  M.  Prindlo's  final  results  have  not  been  published.  Some  account  of  the  geology 
of  this  region  is  contained  in  The  gold  placers  of  the  Fortymile,  Birch  Creek,  and  Fair- 
banks districts:  Bull.  U.  S.  Geol.  Survey  No.  251,  1905,  pp.  23-38. 
c  The  final  report  is  in  preparation.  An  abstract  entitled  "A  reconnaissance  in  the 
Mount  McKinley  region,  Alaska,"  was  published  in  Science,  new  ser.,  vol.  16,  1902,  pp. 
985-986. 
d  Schrader,  F.  C,  A  reconnaissance  along  Chandlar  and  Koyukuk  rivers  :  Twenty-first 
Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  2,  1900,  pp.  471-472. 
e  Spurr,  J.  E.,  A  reconnaissance  in  southwestern  Alaska  :  Twentieth  Ann.  Rept.  TJ.  S. 
Geol.  Survey,  pt.  7,   1900,  pp.  234,  235. 
f  Collier,  A.  J.,  The  geology  of  Yukon  River.     In  preparation. 
v  Grewingk,  C,  Beitrage  zur  Kentnisse  der  orographischen  und  geognostischen  Beschaf- 
fenheit  der  Northwest  Kiiste  Amerikas,  mit  den  anliegenden  Inseln,  St.  Petersburg,  1850. 
AOp.  cit,  pp.  233-234. 
*  Martin,  G.  C,  The  geology  of  Alaska  Peninsula.     In  preparation. 
