696  PRE-CAMBRIAN    GEOLOGY   OF   NORTH   AMERICA. 
Except  a  few  areas  of  granite  and  more  recent  dikes  of  basic  igne- 
ous rocks,  principally  diabase,  the  rocks  have  all  been  profoundly 
altered  and  rendered  more  or  less  completely  schistose.  In  a  few 
instances  recorded  observations  of  bedding  and  banding,  correspond- 
ing to  the  original  bedding  planes,  have  been  noted,  extending  across 
the  schistosity  of  a  part  of  the  schistose  rocks  at  generally  low  angles. 
The  schistosity  of  the  rocks  composing  this  belt  conforms  broadly 
to  a  general  northeast-southwest  strike,  with  steep  dip  to  the  north- 
west. Local  departures  from  these  directions  are  numerous.  This 
belt  composes  Emmons's  Taconic  and  Kerr's  Huronian. 
Complete  differentiation  of  the  rocks  has  not  been  effected,  but 
enough  petrographic  work  has  been  done  to  conclusively  prove  the 
presence  of  considerable  areas  of  sedimentaries.  A  part,  at  least,  of 
the  argillaceous,  sericitic,  and  chloritic  schists  found  within  the  lim- 
its of  the  belt  is  of  sedimentary  origin.  On  the  other  hand,  many 
of  the  so-called  slates  and  schists  originally  classed  as  sedimentary 
by  the  earlier  geologists  are  definitely  proved  to  be  of  igneous  origin. 
Beginning  at  the  Virginia  boundary  to  the  east  of  Danville,  a  belt 
of  typical  ancient  lavas  and  associated  tuffs  of  both  acidic  and  basic 
types  is  traced  across  the  State  into  South  Carolina.  G.  H.  Wil- 
liams recognized  in  the  central  and  northern  portions  of  the  belt 
felsites,  porphyrites,  and  rhyolites,  showing  both  spherulitie  and  flow 
structures,  accompanied  by  pyroclastic  breccias  and  tuffs.  Devitri- 
fied  acidic  glasses  with  chains  of  spherulites  and  eutaxitic  structures 
were  collected  by  Williams.  More  recently  in  the  northern  part  of 
the  same  belt,  with  about  equal  extension  in  Virginia  and  North 
Carolina,  Watson  has  traced  and  described  an  area  of  ancient  ande- 
sitic  (metaandesite)  lavas  and  associated  tuffs,  now  profoundly  altered 
and  rendered  schistose,  which,  in  connection  with  their  other  charac- 
ters, very  closely  resemble  the  typical  greenstones  of  the  Lake  Supe- 
rior region.  Field  and  laboratory  study  refers  these  ancient  lavas 
studied  by  Williams  and  Watson  to  pr'e-Cambrian  age,  probably  con- 
temporaneous with  the  lavas  of  South  Mountain  in  Maryland  and 
Pennsylvania. 
Likewise  recent  study  in  the  same  area  points  to  pre-Cambrian  age 
for  a  part,  at  least,  of  the  granites  and  granite  gneisses  which  occur 
largely  over  the  extreme  northeastern  part  of  the  belt, 
Perhaps  the  principal  area  of  slates  that  can  be  shown  to  be  of 
sedimentary  origin  is  that  extending  over  parts  of  Union,  Albemarle, 
and  Montgomery  counties,  in  the  southern  .portion  of  the  belt.  This 
area  of  slates  was  designated  the  Monroe  slates  by  Nitze;  and  for 
the  reason  that  fossils  were  not  found  in  them  they  were  provision- 
ally referred  by  the  same  author  to  the  Algonkian.  Similarly  the 
siliceous  magnesian  limestones  of  Kings  Mountain,  etc.,  have  been 
provisionally  assigned  by  Nitze  to  the  Algonkian. 
