416  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
SECTION  III.      THE   SOUTHERN  ATLANTIC   STATES. 
LITERATURE   OF   THE    VIRGINIAS. 
Cornelius,174  in  1818,  finds  west  of  the  Secondary  formations  ranges 
of  granites,  schists,  and  other  primitive  rocks.  The  Bine  ridge  is  the 
dividing  line  between  the  granite  and  the  limestone  country  to  the  west- 
ward. 
Eooers  (W.  B.),175  in  1840,  describes  the  southern  district  east  of  the 
Bine  ridge  as  occupied  mostly  by  rocks  of  very  ancient  date,  most  of 
them  believed  to  be  primary.  A  part  of  them  are  in  irregular  masses, 
and  others  have  regular  stratification,  but  all  are  alike  considered  of 
metamori)hic  origin.  Aside  from  these  there  occur  igneous  rocks.  The 
more  important  metamorphic  rocks  are  granite,  syenite,  gneiss,  mica- 
slate,  talc-slate,  argillaceous  slate,  pseudo-  gneiss  or  gneissic  sandstone, 
soapstone  rocks,  micaceous  and  talcose  limestones,  and  marbles.  By 
pseudo-gneiss  or  gneissoid  sandstone  is  meant  rocks  which  resemble  the 
truly  crystalline  rocks,  but  which  plainly  betray  their  sedimentary  ori- 
gin by  the  rounded  character  of  the  quartz  and  other.constituents  which 
compose  them.  The  igneous  rocks  cut  the  shales  and  sandstones  of  the 
Middle  Secondary. 
Sogers  (W.  B.),176  in  1841,  gives  the  geological  occurrences  of  the 
primary  and  metamorphic  rocks.  In  these,  beds  of  limestone  are 
included  at  various  points.  Quartz-slate  and  quartzite  are  found  in  the 
Bull  Eun  mountains  and  other  localities. 
Fontaine,177  in  1875,  describes  several  sections  of  crystalline  rocks 
which  are  regarded  as  pre- Silurian.  Among  them  are  argillite,  green- 
stone, and  syenite.  At  a  tunnel  the  contact  of  the  Silurian  with  the 
argillite  is  beautifully  exposed  and  the  great  contrast  of  the  two  sys- 
tems is  well  shown. 
Fontaine,178  in  1875,  describes  the  central  part  of  the  Blue  ridge  as 
consisting  of  coarse  granites  and  gneisses  of  Laurentian  age.  Along 
the  eastern  slope  of  the  syenite  is  a  formation  of  argillites  which  is  cov- 
ered by  a  series  of  mica-slates,  schists,  and  gneisses.  The  axis  is  occu- 
pied by  talcose  limestones,  quartzites,  mica-slates,  and  hydromica- slates 
which  closely  resemble  those  in  Berkshire  county,  Massachusetts.  In 
this  belt  are  probably  two  systems,  one  older  than  the  Primordial,  and 
the  other  metamorphosed  Silurian.  The  unconformity  which  exists 
between  the  syenite  and  argillite  apparently  shows  the  latter  to  be 
Huronian,  although  its  age  is  not  positively  determined. 
Campbell  (J.  L.),179  in  1879,  states  that  the  Archean  rocks  of  the 
Blue  ridge  are  granite  and  syenite.  They  underlie  the  stratified  rocks 
of  the  region,  but  are  probably  more  recent  than  they,  being  thrown 
upward  through  them.  The  bedded  rocks  resting  upon  the  syenite  are 
much  metamorphosed  and  gneissoid  in  character.  These  are  followed 
by  a  bed  of  conglomeratic  quartzite  and  slates,  upon  which  lie  uncon- 
formably  the  Primordial  rocks. 
