PIEDMONT  PLATEAU  AND  PORTIONS  OF  THE  APPALACHIANS.       701 
Clements,  in  a  microscopical  study  of  certain  rocks  from  the  crystal- 
line area  of  Alabama,  includes  sedimentary  and  igneous  rocks,  and 
others  whose  origin  is  unknown.  Disregarding  the  sedimentary 
rocks,  which  are  comparatively  unimportant,  Clements  regards  the 
rocks  as  a  whole  as  having  characters  of  Archean  rocks. 
In  1894  Smith  published  a  geological  map  of  Alabama  with  an 
explanatory  chart,  in  which  the  rocks  of  the  crystalline  area  are 
mapped  and  described  under  two  series.  The  older,  characterized  as 
fully  crystalline  and  comprising  mainly  crystalline  schists,  is  referred 
to  the  Archean.  The  younger,  characterized  as  imperfectly  crystal- 
line and  comprising  altered  sediments,  is  named  the  Talladega  or 
Ocoee,  and  is  provisionally  referred  to  the  Algonkian.  The  classifica- 
tion of  the  Talladega  is  marked  as  uncertain,  probably  in  part  Cam- 
brian. 
In  the  northwestern  part  of  the  Ashland  quadrangle,  in  north- 
eastern Alabama,  fossils  have  been  found  in  black  shale  which  had 
been  previously  considered  as  Ocoee.  The  black  shale  is  associated 
with  Ocoee  rocks,  but  from  the  evidence  cited  above  it  will  possibly 
prove  to  be  Carboniferous  and  can  be  correlated  with  a  great  thick- 
ness of  black  shale  to  the  northwest  in  Georgia. 
Keith,108  in  1905,  summarizes  the  pre-Cambrian  geology  of  the 
southern  Appalachians. 
General  relations. — Among  the  earlier  students  the  Appalachian 
Province  was  tacitly  limited  to  the  Paleozoic  rocks.  The  rocks  which 
lie  southeast  of  them  are  in  the  main  older  and  more  or  Less  meta- 
morphosed. In  the  latter,  however,  typical  Appalachian  folds  and 
faults  are  found  wherever  the  formations  are  in  contrast.  In  the 
Paleozoic  sediments,  likewise,  large  masses  of  rock  are  metamorphic. 
The  Appalachian  Mountains  are  made  up  of  the  lowest  Paleozoic 
rocks  and  various  older  rocks  of  igneous  or  metamorphic  nature. 
Over  the  Piedmont  Plateau,  which  joins  the  mountains  on  the  south- 
east, many  sedimentary  rocks  are  folded  in  between  the  metamorphic 
beds.  Wherever  they  have  been  closely  studied  these  sediments  are 
of  Cambrian  or  later  age,  and  it  seems  highly  probable  that  most  of 
the  less  studied  sediments  are  of  similar  age.  The  igneous  formations 
of  the  Piedmont  are  the  same  as,  and  often  continuous  with,  the 
igneous  rocks  of  the  Mountains.  From  a  geological  point  of  view, 
therefore,  there  is  no  distinction  between  the  Piedmont  and  the  Ap- 
palachian Mountains,  however  much  they  diverge  as  topographic 
features. 
A  brief  synopsis  is  here  given  of  the  pre-Cambrian  formations  in 
order  of  aire.  More  detailed  descriptions  of  them  will  be  found  in 
the  Harpers  Ferry,  Washington,  Cranberry,  Asheville,  Greeneville, 
Mount  Mitchell,  Xantahala.  Roan  Mountain,  and  Pisgah  folios  of  the 
