VANHtsE.J  EASTERN    UNITED    STATES.  .421 
and  gneisses  rocks  which  are  extremely  metamorphosed.  These  rocks, 
as  well  as  the  slates  and  schists,  belong  to  the  most  ancient  of  the 
Azoic  series,  and  the  Black  mountains  are  the  oldest  part  of  this 
Azoic. 
Kerr,  ,92  in  1875,  gives  a  systematic  account  of  the  geology  of  North 
( Carolina.  The  Azoic  rocks  are  divided  into  Huronian,  Laurentian,  and 
Igneous.  With  the  Huronian  are  placed  the  siliceous  and  argillaceous 
slates  and  conglomerates,  micaceous  and  hornblendic  slates  and  schists, 
chlorites,  quartzites  and  diorites,  with  eherty,  jaspery  and epidotie  beds, 
and  much  specular  iron  ore.  The  Laurentian  includes  gneiss,  granite, 
hornblende  slates,  etc.,  while  the  Igneous  includes  granite,  syenite, 
porphyry,  etc. 
The  Laurentian  occurs  in  four  areas.  The  .Ealeigh  area  is  a  belt  20 
or  25  miles  wide,  running  northeast  from  this  place  to  the  state  line, 
and  consisting  of  light  colored  and  gray  gneisses  which  occasionally 
pass  into  granite.  These  are  cut  by  coarse  syenite  and  diorite  dikes. 
The  second,  the  Salisbury  granite  area,  is  from  10  to  30  miles  wide,  and 
lias  an  area  of  about  3,000  square  miles.  The  prevalent  rocks  are 
syenite,  dolerite,  greenstone,  amphibolite,  granite,  porphyry,  and  tra- 
chyte. In  it  there  is  no  well  defined  gneiss,  mica-slate,  serpentine, 
or  limestone.  The  large  area  of  Mecklenburg  syenite  is  regarded  as 
the  oldest  rock  of  North  Carolina,  the  bottom  of  the  Laurentian.  West 
of  the  Salisbury  area  is  the  largest  connected  area  of  Laurentian  in  the 
state,  covering  not  less  than  16,000  square  miles.  It  closely  resembles 
the  Raleigh  area,  especially  in  the  southeastern  part,  where  it  consists 
of  a  succession  of  schists,  gneisses,  and  slates,  for  the  most  part  thin 
bedded,  and  only  occasionally  showing  granite-like  masses  and  syenites 
which  are  generally  in  the  forms  of  dikes.  Belonging  with  this  series 
are  probably  the  interstratified  crystalline  limestones  of  Forsyth,  Yad- 
kin, and  Stokes.  The  outcrops  are  generally  limited  to  two  or  three 
rods  in  thickness,  a  few  hundred  yards  in  length,  and  seem  to  graduate 
into  the  neighboring  gneisses.  The  fourth  considerable  area  of  Lauren- 
tian rocks,  occupying  an  area  of  3,000  or  4,000  square  miles,  is  west  of 
the  Blue  ridge,  between  this  range  and  the  Smoky  mountains.  This  is 
probably  a  continuation  of  the  preceding  belt,  being  separated  from  it 
by  a  narrow  belt  of  Huronian  slates,  and  like  it  containing  crystalline 
limestones. 
The  Huronian  follows  the  Laurentian  without  a  break  of  geological 
continuity.  These  rocks  are  found  in  five  principal  lines  of  outcrops. 
These  are  that  east  of  the  Ealeigh  Laurentian,  that  between  the  Ra- 
eigh  and  Salisbury  granite,  that  west  of  the  Salisbury  granite  or 
King's  mountain  belt,  that  of  the  Blue  ridge  mountains,  and  that  of 
}he  great  Smoky  mountains,  called  the  Cherokee  slates.  These  belts 
ire  placed  with  the  Huronian  because  they  succeed  the  Laurentian, 
iinl  because  they  differ  from  them  in  degree  of  metamorphism  and 
ithological  character,  so  that  the  change  from  one  to  the  other  is  ob- 
