PIEDMONT  PLATEAU  AND  PORTIONS  OF  THE  APPALACHIANS.       099 
recent  years,  and  we  arc  largely  dependent  at  present  upon  the  work 
of  the  earlier  geologists — Tuomey  and  Lieber.  A  similar  complex 
of  altered  igneous  masses  and  some  associated  metamorphic  sediments, 
described  for  the  adjacent  parts  of  North  Carolina  and  Georgia,  and 
in  part  of  pre-Cambrian  age,  makes  up  the  corresponding  parts  of 
the  South  Carolina  Piedmont  areas.  The  rocks  are  essentially  of  the 
same  types  as  in  the  other  States  where  much  detailed  work  has  been 
done,  comprising  chiefly  granites,  gneisses,  schists,  slates,  sandstones, 
and  limestones,  all  greatly  altered,  and  associated  with  some  basic 
eruptive  materials.  G.  H.  Williams  mapped  and  described  several 
small  areas  of  probable  pre-Cambrian  volcanics  over  parts  of  the 
South  Carolina  Piedmont  region  similar  to  those  of  North  Carolina. 
Georgia. — According  to  Hayes  the  southeastern  portion  of  Bartow 
County,  in  northwest  Georgia,  is  about  equally  divided  between  the 
older  crystalline  and  metamorphic  rocks  of  the  Piedmont  Plateau 
and  the  Appalachian  Mountains  on  the  east  and  the  Paleozoic  (Cam- 
bro-Silurian)  sediments  of  the  Appalachian  Valley  on  the  west.  The 
Paleozoic  sediments  are  referred  to  Cambro-Silurian  age.  To  the 
east  and  south  of  the  Paleozoic  sediments  are  the  metamorphic  crys- 
talline rocks  of  the  Piedmont  area,  which  include  slates,  schists,  con- 
glomerates, gneiss,  and  granite.  The  oldest  of  these  rocks  is  the 
granite,  which  is  mapped  as  pre-Cambrian.  The  conglomerate,  slate, 
and  schist  are  mapped  as  Ocoee,  which  is  referred  to  the  Algonkian, 
for  the  reason  that  no  fossils  were  found  in  them  and  because  they 
have  every  appearance  of  extreme  age.  The  coarse  conglomerate  bor- 
dering the  granite  was  unquestionably  derived  from  the  granite. 
Where  not  bordered  by  the  coarse  conglomerate  the  granite  is  in 
contact  with  black  graphitic  slates,  which  generally  overlie  the  coarser 
sediments. 
In  this  area  the  rocks  of  the  Ocoee  series  generally  show  an  in- 
creasing degree  of  metamorphism  toward  the  southeast;  and  within 
a  few  miles  of  this  region  they  pass  into  schists  and  gneisses,  the 
original  form  of  which,  whether  igneous  or  sedimentary,  can  not  be 
readily  determined.  This  increased  metamorphism  toward  the  south- 
east is  due  in  part  to  the  greater  compression  which  that  region  has 
suffered  and  in  part  to  the  presence  of  considerable  bodies  of  various 
igneous  rocks  which  have  been  intruded  into  the  sedimentary  beds. 
The  intrusive  rocks  present  a  considerable  variety  in  composition. 
varying  from  extremely  basic  diabase  to  acidic  granites.  The  most 
common  variety  is  diorite,  which  Avas  among  the  earlier  intrusions, 
and  has  been  subsequently  converted  for  the  most  pari  into  amphib- 
olite  schist.  The  extreme  southeast  corner  of  the  mapped  area  is 
occupied  by  the  Acworth  gneiss,  which,  like  the  Corbin  granite,  is 
probably  Archean  in  age,  and  formed  the  foundation  <>u  which  the 
oldest  sediments  of  the  region  were  deposited. 
