698  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
are  all  of  igneous  origin  and  appear  to  be,  in  large  part,  of  surface 
volcanic  nature. 
The  Carolina  portion  of  the  Asheville  quadrangle  comprises  mainly 
granites  and  gneisses,  the  latter  of  undetermined  origin  but  prob- 
ably derived  from  basic  intrusives.  Both  the  granites  and  the 
gneisses  are  mapped  and  classed  as  Archean.  Dikes  of  rhyolite,  peg- 
matite, quartz  diorite,  basalt,  and  dunite,  with  its  derivatives  talc 
and  serpentine,  are  numerous.  Lenticular  beds  of  siliceous  marble 
occur  in  the  gneiss,  indicating  a  probable  sedimentary  origin  for 
parts  of  it.  The  Archean  rocks  mapped  and  described  are  Carolina 
gneiss;  Roan  gneiss;  metagabbro;  soapstone,  dunite,  and  serpentine; 
Cranberry  granite,  and  Max  Patch  granite.  Metadiabase  and  meta- 
rhyolite  are  mapped  as  doubtful  Algonkian.  (See  also  summaries 
of  Mount  Mitchell  and  Nantahala  folios,  pp.  683,  684.) 
Tennessee. — Within  recent  years  much  of  the  geology  of  eastern 
Tennessee,  including  the  mountain  areas,  has  been  mapped  and  de- 
scribed by  geologists  of  the  United  States  Geological  Survey — prin- 
cipally Keith  and  Hayes.  The  pre-Cambrian  masses,  largely  igneous 
but  jurobably  sedimentary  in  part,  mapped  and  described  by  Keith 
in  the  Cranberry  and  Asheville  folios,  extend  from  North  Carolina 
into  Tennessee. 
Three  of  the  quadrangles — the  Knoxville,  Loudon,  and  Cleveland — 
include  in  the  mountain  areas  a  series  of  sediments  known  as  the 
Ocoee,  of  unknown  age.  The  Ocoee  rocks  comprise  bluish-black  and 
gray  argillaceous  and  calcareous  slates  and  coarse  and  fine  quartz 
conglomerate  and  sandstone.  The  formations  contain  so  few  con- 
stant characteristics  and  undergo  so  many  variations  that  correlation 
is  very  difficult.  No  fossils  have  yet  been  found  in  these  rocks.  Ac- 
cording to  Hayes  the  rocks  of  the  Ocoee  series  bear  all  the  marks  of 
extreme  age,  and  for  this  reason  as  much  of  the  Ocoee  as  was  included 
in  the  Cleveland  quadrangle  was  provisionally  assigned  as  probable 
Algonkian,  until  more  satisfactory  evidence  of  the  age  of  the  rocks 
could  be  found.  In  earlier  publications  the  Ocoee  rocks  were  con- 
sidered to  be  Cambrian  and  to  lie  under  the  Chilhowee  rocks  (Cam- 
brian), but  according  to  Keith  there  is  ample  evidence  that  they 
should  be  separated  from  the  Cambrian  in  the  Tennessee  area,  though 
it  is  not  sufficient  to  fix  their  age. 
In  the  quadrangles  where  there  are  mapped  and  described  the  Ocoee 
series  of  unknown  age,  the  oldest  rocks,  definitely  fixed  by  the  find- 
ing of  fossils  in  some  of  the  formations,  are  Cambrian.  The  Cam- 
brian formations  are  all  of  sedimentary  origin,  except  a  thin  basaltic 
flow  in  the  Cranberry  region,  and  comprise  conglomerates,  sandstones, 
shales,  and  limestones. 
South  Carolina. — Our  knowledge  of  the  crystalline  rocks  composing 
the  Piedmont  region  of  South  Carolina  has  not  been  increased  in 
