PIEDMONT  PLATEAU  AND  PORTIONS  OF  THE  APPALACHIANS.      677 
Chester,01  in  1890,  describes  the  gabbros,  gabbro  diorites,  and 
hornblende  schists  of  Delaware  and  their  relations  to  the  surround- 
ing rocks.  The  gabbro,  gabbro  diorites.  and  hornblende  schists  are 
found  to  grade  into  one  another  by  imperceptible  stages;  the  two 
latter  are  regarded  as  a  metamorphosed  product  of  the  former,  and 
all  as  of  igneous  origin.  These  rocks  are  found  at  various  points  in 
contact  with  the  mica  schists  and  gneisses.  Where  the  eruptive  rocks 
have  a  schistose  structure,  this  is  in  apparent  conformity  with  the 
foliation  of  the  mica  schists.  Sometimes  the  mica  schists  appear  to 
dip  beneath  the  eruptive  rocks,  and  at  other  times  to  overlie  them. 
No  evidence  was  found  of  any  bedding  not  coincident  will)  the  cleav- 
age. The  unconformity  discovered  by  Hall  between  the  trappean 
rocks  and  the  mica  schists  in  Delaware  County.  Pa.,  was  not  found 
on  the  Delaware  side  of  the  line.  If  the  horizontal  bedding  de- 
scribed exists,  it  is  so  obscured  as  to  be  unrecognizable;  if  the  mica 
schists  are  considered  to  lie  horizontal,  the  eruptive  character  of  the 
gabbros,  gabbro  diorites,  and  hornblende  rocks  is  but  the  more  evident. 
SECTION  5.     NORTH  CAROLINA. 
SUMMARY   OF  LITERATURE. 
Olmsted,62  in  1824,  describes  as  parallel  with  the  freestone  and 
coal  formations  a  great  slate  formation,  about  20  miles  wide,  which 
extends  across  the  State  from  northeast  to  southwest,  running  through 
Person,  Orange,  Chatham,  Randolph,  Montgomery,  Cabarrus,  A.nson, 
and  Mecklenburg  counties.  Within  this  district  are  found  numerous 
beds  of  porphyry,  soapstone,  serpentine,  greenstone,  and  whetstone. 
From  Halifax  to  Person  court-house  hardly  any  kind  of  rock  but 
granite  is  met. 
Olmsted,63  in  1825,  more  fully  describes  the  great  slate  formation, 
which  includes  argillite,  greenstone,  porphyry,  novaculite,  petrosilex, 
hornstone,  black  steatite,  syenite,  etc.  Between  the  great  slate  forma- 
tion and  the  Blue  Ridge  are  a  granitic  district,  various  limestone  \hh\s, 
and  a  Transition  formation.  The  granitic  district  occupies  the  whole 
country,  with  subordinate  exceptions,  from  the  slate  formation  to  the 
Blue  Ridge.  The  term  granitic,  as  here  used,  embraces  gneiss  and 
mica  shite  as  well  as  granite.  Among  the  subordinate  beds  none  are 
so  numerous  as  greenstone.  In  Stokes  and  Surrey,  in  connection  with 
the  iron  ores,  are  numerous  isolated  beds  of  limestone  which  lie  in 
mica  slate  rocks. 
Mitchell,64  in  1820,  states  that  of  the  Primitive  rocks  of  North 
Carolina  the  more  ancient  lie  farther  west  and  the  more  recent  in  the 
midland  counties.  Those  of  the  eastern  division  are  highly  crystalline 
in  structure,  consisting  of  gneiss,  slate,  and  schist,  with  some  granite, 
while  those  of  the  western  division  are  almost   exclusively  granite. 
