708  PKE-CAMBEIAN    GEOLOGY    OF    NORTH   AMERICA. 
rocks,  comprising  conglomerates,  quartzites,  quartz  schists,  mica 
schists,  slates,  and  limestones,  the  age  of  which  is  very  difficult 
to  determine.  These  belts  of  sediments  vary  in  length  and  breadth 
from  those  which  are  comparatively  narrow  and  extend  a  few 
miles  to  a  great  belt  called  the  Ocoee  group  by  Safford,  which  has 
a  maximum  width  of  25  miles  or  more  and  which  extends  areally 
from  North  Carolina  and  Tennessee  to  Alabama.  The  great  Ocoee 
belt  comprises  a  large  part  of  the  great  Unaka  Mountains,  but  in  its 
southwestward  extension  passes  onto  the  relatively  low  lands  of  Ala- 
bama. At  the  northeastern  end  of  the  area  the  rocks  are  less  altered 
than  in  the  southwestern  part.  The  Ocoee  rocks  in  the  unmetamor- 
phosed  district  consist  predominantly  of  conglomerates,  quartzites, 
and  slates  with  limestones,  and  in  the  metamorphosed  districts  these 
have  been  transformed  to  conglomerate  schists,  graywackes,  quartz 
schists,  mica  schists,  mica  slates,  and  marbles. 
Many  of  the  minor  belts  of  sediments  occur  upon  the  Piedmont 
Plateau  in  the  Virginias,  the  Carolinas,  and  Georgia.  In  many  places 
these  belts  are  so  extremely  metamorphosed  that  they  now  show  no 
evidence  of  fossils,  if  they  once  possessed  them.  Indeed,  the  meta- 
morphism  has  destroyed  all  clastic  characters.  AVhile  it  has  not 
been  proved,  it  is  very  probable  that  many  of  these  belts  belong  to  the 
same  period  as  the  great  Ocoee  group ;  thus  the  determination  of  the 
age  of  the  Ocoee  is  of  the  greatest  importance. 
The  age  of  the  Ocoee  group  is  a  problem  to  which  the  attention  of 
American  geologists  has  been  directed  for  more  than  a  quarter  of  a  cen- 
tury, and  even  at  the  present  time  its  answer  is  not  altogether  clear. 
In  the  area  where  the  Ocoee  has  been  most  closely  studied,  in  North 
Carolina,  Tennessee,  and  Georgia,  Keith  has  reached  the  conclusion 
that  the  entire  group  is  of  Cambrian  age.  He  divides  his  Cambrian, 
from  the  base  up,  into  the  Snowbird  formation,  the  Hiwassee  slate,  the 
Cochran  conglomerate,  the  Nichols  slate,  the  Nebo  quartzite,  the  Mur- 
ray slate,  the  Hesse  quartzite,  above  which  is  the  Shady  limestone. 
Above  the  Shady  limestone  follow  other  conformable  formations  of  the 
Cambrian.  The  Olenellus  fauna  has  been  discovered  as  low  as  the 
Nichols  slate.  The  formations  which  are  certainly  Cambrian  are  con- 
formable with  the  lower  formations  of  the  Ocoee,  and  the  upper  part  of 
the  Ocoee  is  stratigraphically  equivalent  to  the  known  Cambrian.  The 
series  as  a  whole,  however,  goes  down  several  thousand  feet  below  any 
discoverable  fossils,  and  in  this  thickness  contains  at  various  places 
blue  and  gray  limestones  so  little  metamorphosed  that  one  would 
expect  to  find  fossils  in  them,  but  the  closest  search  by  Walcott  and 
many  others  has  failed  to  reveal  a  single  trace  of  any  organic  form. 
The  question  arises  as  to  what  part  of  the  Ocoee  rocks  is  truly  pre- 
Olenellus  or  Algonkian.  About  one-half  seems  to  be  of  this  age  ac- 
cording to  present  knowledge.    So  far  as  the  Ocoee  is  Algonkian  the 
