PIEDMONT  PLATEAU  AND  PORTIONS  OF  THE  APPALACHIANS.       693 
Gold  ores  are  associated  with  both  the  sedimentary  and  the  igne- 
ous series.    Their  mode  of  occurrence  is  briefly  sketched. 
Brooks,10"'  in  1896,  in  petrographic  notes  on  sonic  metamorphic 
rocks  from  Alabama,  makes  general  statements  concerning  the  geol- 
ogy of  the  metamorphic  rocks  of  Alabama  and  Georgia.  The  meta- 
morphic rocks  of  Alabama  and  Georgia  may  be  differentiated  into 
two  series.  The  older,  or  crystalline  series,  includes  crystalline 
schists  and  gneisses,  whose  origin  is  doubtful,  together  with  large 
masses  of  gneissoid  granite.  The  younger,  or  clastic  series,  is  typically 
made  up  of  phyllites,  sericite  schists,  chlorite  schists,  conglomerates, 
quartzites,  crystalline  sandstones,  and  in  a  portion  of  the  region  lime- 
stones and  marbles.  The  rocks  of  both  series  are  closely  associated 
with  rocks  of  undoubted  igneous  origin. 
SECTION    10.     SOUTHERN   PIEDMONT  AND  APPALACHIAN 
REGIONS  (GENERAL). 
SUMMARY  OF  LITERATURE. 
Britton,100  in  1886,  describes  the  contact  at  Natural  Bridge  be- 
tween sandstones  which  appear  to  be  under  the  Potsdam  and  over 
the  Archean.  The  two  are  widely  unconformable:  the  sandstone  dips 
45°  NW.  and  strikes  N.  40°  E.,  while  the  Archean  dips  65  E.  and 
strikes  N.  5°  E.  The  Archean  rocks  consist  of  quartz-bearing  syenite 
and  granulite,  fragments  of  which  are  found  in  the  overlying  series. 
On  Doe  River,  in  eastern  Tennessee,  the  Archean  and  basal  Silurian 
quartzite  are  in  contact.  The  Archean  is  a  pegmatite,  with  no 
bedding  or  lamination.  Five  hundred  feet  east  of  the  contact  it  is 
a  much  contorted  hornblendic  gneiss  and  syenite.  These  rocks  are 
intersected  by  a  trap  dike.  The  quartzite  is  thickly  bedded  and  con- 
tains many  pebbles  of  quartz  and  much  feldspar,  so  as  to  make  the 
rock  in  places  an  arkose. 
On  French  Broad  River  are  found  quartzites  like  those  of  Doe 
River,  which  are  succeeded  by  basal  crystalline  rocks,  and  near 
Marshall  station  begins  a  stratified  micaceous  schistose  series.  The 
character  of  the  transition  between  this  and  the  basal  Archean  rocks 
was  not  apparent.  About  Asheville  are  well-bedded  gneisses  and 
mica  schists  which  bear  the  same  relation  to  the  heavily  bedded  basal 
Archean  as  do  the  Westchester  County,  X.  Y.,  and  Philadelphia 
gneisses  to  the  basal  rocks  farther  west.  These  rocks  extend  to  tin1 
top  of  Mount  Mitchell. 
Watson,107  in  L905,  summarizes  the  pre-Cambrian  geology  of  the 
southern  Appalachians. 
Virginia. — The  work  of  the  Tvoo-ers  Survey,  covering  the  years 
is:;:*  to  L841,  inclusive,  comprises  the  only  geologic  work  thai  has 
yet  been  done  in  Virginia  on  the  pre-Cambrian.    The  more  important 
