700  PftE-CAMBRTAN    GEOLOGY  OF   NORTH   AMERICA. 
According  to  Watson  granites  and  granite  gneisses  have  wide  dis- 
tribution over  the  Georgia  Piedmont  region.  The  two  types  differ 
only  in  the  more  marked  foliated  structure  of  the  granite  gneiss.  As 
a  ride  the  contorted  gneiss  phase  is  not  traced  into  the  massive  type 
of  the  granite.  Field  and  laboratory  study  indicates  that  at  least  two 
distinct  periods  of  intrusion  of  closely  similar  acidic  material  are 
represented  in  the  Georgia  area.  Most,  if  not  all,  of  the  granitic 
masses  studied  are  believed  to  be  pre-Cambrian,  though  some  may 
possibly  be  later. 
A  number  of  thin  bands  of  magnesian  limestone  and  larger  areas 
of  sandstone  or  quartzite  occur  in  places  over  parts  of  the  Georgia 
Piedmont  region.  The  entire  or  exact  significance  of  these  sedimen- 
tary masses,  especially  their  age  and. their  relations  to  the  associated 
rocks,  has  not  yet  been  determined.  While  King  referred  the  rocks 
of  the  entire  "  Crystalline  belt  "  of  Georgia  to  pre-Cambrian  age,  it 
is  probable  that  careful  study  of  the  region  will  reveal  a  post-Algon- 
kian  age  for  at  least  a  part  of  the  sedimentaries,  including  the  lime- 
stones and  quartzites  mentioned  above. 
Alabama. — Smith  describes  the  rocks  composing  the  crystalline 
area  in  northeastern  Alabama  as  including  altered  sedimentaries  and 
igneous  masses.  The  altered  sedimentary  rocks,  called  the  Talladega 
or  Ocoee  series,  are  referred  to  the  Algonkian,  and  the  altered  igneous 
rocks  are  referred  to  the  Archean.  The  Talladega  or  Ocoee  series 
occurring  in  the  northeastern  part  of  the  State  in  four  or  five  roughly 
parallel  belts  trending  northeast-southwest  and  having  a  general 
southeast  dip,  comprises  argillites,  graphitic  in  places,  quartzites  and 
quartzite  conglomerates,  and  crystalline  limestones  or  dolomites.  The 
slates,  quartzites,  and  conglomerates  closely  resemble  certain  strata  of 
undoubted  Cambrian  age,  and  it  is  probable  that  some  of  the  strata 
included  in  the  Talladega  will  prove  to  be  altered  Cambrian  rocks. 
Fossils  have  not  yet  been  discovered  in  them. 
The  altered  igneous  rocks  referred  to  the  Archean  are  grouped  in 
three  main  belts  roughly  paralleling  the  sedimentary  belts  of  the 
Talladega  series.  They  comprise  gneisses  and  mica  schists,  cut  by 
dikes  of  granite,  diorite,  and  various  hornblendic,  pyroxenic,  and 
chrysolitic  rocks. 
Brooks,  in  petrographic  notes  on  some  metamorphic  rocks  from 
Alabama,  differentiates  the  metamorphic  rocks  of  Georgia  and  Ala- 
bama into  two  series.  The  older,  or  crystalline  series,  includes  crystal- 
line schists  and  gneisses  of  doubtful  origin  and  large  masses  of  gneis- 
soid  granite.  The  younger,  or  clastic  series,  is  typically  made  up 
of  phyllites,  sericite  schists,  chlorite  schists,  conglomerates,  quartz- 
ites, crystalline  sandstones,  and  in  places  limestones  and  marbles. 
The  rocks  of  both  series  are  closely  associated  with  rocks  of  undoubted 
igneous  origin. 
