56  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA.^ 
graphic  relations  are  not  precisely  the  same,  correlation  is  not  estab- 
lished. 
The  strata  of  the  Hu-t'o  series  and  the  Nan-k'ou  limestone  closely 
resemble,  in  siliceous  and  calcareous  character  and  in  the  very  mod- 
erate degree  of  alteration  which  they  have  suffered,  the  Belt  series 
of  Montana.  No  fossils  have  been  found  in  them,  but  it  is  not  im- 
possible that  further  search  may  be  successful. 
From  the  researches  of  Richthofen,  Loczy,  Obrutchoff,  and  others 
it  is  known  that  pre-Cambrian  rocks  occur  in  many  other  mountain 
ranges  in  China.  In  some  cases  only  the  basal  complex  appears  to 
be  represented,  while  in  others  metamorphosed  sedimentary  strata 
have  been  observed. 
According  to  Willis  " — 
A  provisional  classification  of  the  Wu-t'ai  and  limiting  systems  in  the  type 
locality  is  as  follows : 
fTung-yii  limestoneJ  Slates,     limestone,     and 
[Tou-ts'un  slate J       qnartzite. 
Hu-t'o  series    (neo-Proterozoic) 
Unconformity. 
Wu-t'ai  series    (eo-Proterozoic) < 
Si-t'ai  group Chiefly   chlorite   schist; 
quartzite    conglomer- 
ate at  the  base. 
Unconformity. 
Xan-t'ai  group Siliceous  marble,  quartz- 
ite, and  schist. 
Unconformity. 
Sh'f-tsui  group Mica       schist,       gneiss, 
magnetite  quartzite, 
and  basal  feldspathic 
quartzite. 
Unconformity. 
T'ai-shan  complex  (Archean) Basal  complex  of  va- 
ried gneisses  and 
younger   intrusives. 
It  has  been  seen  that  the  Archean,  or  basement  complex,  consists 
dominantly  of  gneisses,  probably  in  large  part  derived  from  igneous 
rocks.  Within  these  gneisses  are  various  intrusions,  among  which 
granite  predominates.  Very  subordinate  masses  of  sedimentary  ma- 
terials are  found.  In  short,  the  descriptions  of  this  complex  show 
that  it  has  all  of  the  characteristics  of  the  Archean.  The  four  sedi- 
mentary groups  unconformably  above  the  Archean  are  composed  of 
rocks  which  were  originally  muds,  grits,  conglomerates,  and  lime- 
stones. In  other  words,  they  have  all  of  the  characteristics  of  the 
Algonkian. 
There  is  thus  a  remarkable  similarity  between  the  Archean  and  the 
Algonkian  of  China  and  similar  systems  in  North  America.    Indeed, 
n  Willis,  Bailey,  and  Blackwelder,  Eliot,  Research  in  China,  vol.  1,  Descriptive  geology, 
pp.  109-123 ;  vol.  2,  Systematic  geology,  p.  4,  Carnegie  Inst.,  1907. 
