684  PRE-CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA. 
rocks;  converting  thorn  into  schists.  Volcanic  rocks,  mainly  repre- 
sented by  bedded  tufts,  covered  these  metamorphosed  rocks  in  places 
and  were  themselves  subjected  to  a  part  of  the  metamorphosing  in-  ; 
fluences.  Into  these  metamorphic  rocks  later  igneous  material  has 
been  intruded.  Granite  is  the  most  abundant  of  these  igneous  rocks, 
and  the  numerous  dikes  of  pegmatite  are  probably  closely  connected 
with  it.  Diabase  dikes  cutting  all  the  foregoing  rocks  are  the  last 
representatives  of  intrusion.  On  the  eastern  border  of  the  area  the 
solid  rocks  are  covered  by  thin  beds  of  sand,  which  probably  belong 
to  the  Coastal  Plain  formations. 
It  seems  probable  that  the  rocks  of  this  area  .belong  to  the  same 
pre-Cambrian  complex  as  those  of  the  Cranberry  district  to  the  north- 
west, and  arc  assigned  to  the  pre-Cambrian.  The  major  subdivisions 
are  similar  to  those  mapped  by  Keith  in  the  Cranberry  and  other 
areas. 
Keith,77  in  1907.  describes  and  maps  the  rocks  of  the  Nantahala 
quadrangle,  in  North  Carolina  and  Tennessee.  The  rocks  assigned  to 
the  pre-Cambrian  occupy  the  southeastern  part  of  the  quadrangle. 
The  oldest  formation  is  the  Carolina  gneiss,  consisting  of  mica  schist 
and  mica  gneiss,  of  unknown  origin.  Intrusive  into  this  are  granite, 
gneiss,  diorite,  and  other  rocks.  Resting  upon  it  unconformably  are 
sandy  sediments  referred  to  the  Cambrian.  Olenellus  fauna  are 
found  in  adjacent  quadrangles  as  far  as  the  middle  of  the  group.  The 
Great  Smoky  conglomerate  and  the  Hiwassee  slate  are  the  format  ions 
supposedly  below  the   Olenellus  horizon. 
Keith,78  in  1907,  maps  and  describes  the  geology  of  the  Roan  Moun- 
tain quadrangle,  in  Tennessee  and  North  Carolina.  Pre-Cambrian 
metamorphic  and  igneous  rocks  occupy  the  southeastern  portion  of 
the  area,  the  metamorphics  as  a  whole  lying  to  the  southeast  of  the 
igneous  areas.  The  oldest  rocks  are  the  Carolina  gneiss,  consisting 
principally  of  mica  gneiss  and  mica  schist  of  unknown  origin.  In- 
trusive into  this  are,  in  order  of  age,  the  Roan  gneiss,  soapstone, 
dunite  and  serpentine  intrusives,  Cranberry  granite,  and  Peech 
granite,  all  much  metamorphosed  under  deep-seated  conditions.  Rest- 
ing unconformably  upon  them  with  obviously  a  great  time  interval 
are  surface  lavas,  called  the  Linville  metadiabase  and  metarhyolite, 
constituting  a  great  series  of  small  dikes  and  sheets  that  are  too  small 
to  be  separately  shown  on  the  map.  The  break  between  them  and  the 
Archean  is  believed  to  be  more  important  than  that  separating  them 
from  the  Cambrian,  and  they  are  therefore  provisionally  classed  as 
Algonkian.  A  great  southeastward-dipping  thrust  fault  Was  devel- 
oped before  the  Appalachian  folding,  and  this  fault  plane  was  further 
folded  and  faulted  during  Appalachian  folding. 
