190  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  260 
S.  C.  It  took  place  so  long  ago  that  the  crest  has  been  worn  away, 
but  its  topographic  effects  are  seen  in  the  two  parallel  ridges  which 
mark  the  position  of  the  quartzite  beds.  Blacksburg  lies  between! 
these  two  ridges.  Kings  and  Crowders  mountains  represent  the 
eastern  outcrop  of  the  quartzite  layer.  The  ridges  are  discontinuous 
and  unsymmetrically  developed  with  respect  to  the  axis  of  the  fold, 
so  it  is  evident  that  relative  resistance  of  the  rocks  and  original 
structure  were  not  the  only  elements  which  entered  into  the  physio- 1 
graphic  development  of  the  region. 
These  original  sediments  have  been  invaded  at  several  times  by 
intrusions  of  igneous  rocks.  Possibly  before  any  intense  metal 
morphism  took  place,  and  certainly  before  it  ceased,  comparatively 
large  massos  of  basic  dioritic  or  gabbroitic  rock  were  intruded 
These  are  now  represented  by  a  dark  greenish  rock,  composed  verjl 
largely  of  hornblende,  which  may  be  called  amphibolite.  A  folia- 
tion has  been  induced  in  the  rock,  and  this  generally  corresponds 
with  the  bedding  of  the  sediments.  Very  much  more  recently  nar- 
row dikes  of  diabase  have  been  erupted,  usually  cutting  across  the 
strike  of  the  older  rocks.  These,  below  the  zone  of  weathering,  are 
practically  unaltered. 
Of  uncertain  age,  but  decidedly  later  than  the  folding  of  the  sedi- 
ments, is  a  biotite-granite  which  approximately  parallels  the  fold. 
It  is  best  exposed  on  the  west  side  of  the  anticline,  but  is  also  known* 
in  places  on  the  east  side. 
Numerous  dikes  of  pegmatite  cut  through  both  the  amphibolite 
and  the  sediments.  These  masses  usually,  but  not  always,  have  the! 
same  or  nearly  the  same  strike  and  dip  as  the  surrounding  rocks. 
The  pegmatite  is  the  formation  which  is  of  interest  in  connection  with; 
the  tin  deposits,  for  in  intimate  association  with  some  of  it  the  ore  is^ 
found. 
DISTRIBUTION  AND  STRUCTURE  OF  THE  TIN-BEARING  ROCK. 
The  tin  belt  is  limited  to  the  occurrence  of  pegmatite.  In  most'j 
places,  so  far  as  at  present  known,  the  belt  is  narrow,  comprising  one 
or  a  few  closely  spaced  dikes.  In  some  localities,  however,  the  nunn 
ber  of  pegmatite  bodies  increases,  and  at  times  also  the  distance 
between  them  is  greater  and  the  belt  is  wider.  This  pegmatite  belli! 
passes  through  Gaffney,  S.  C,  northwest  of  Blacksburg,  S.  C,  just l 
southeast  of  the  towns  of  Grover  and  Kings  Mountain,  N.  C,  a.i 
couple  of  miles  west  of  Bessemer,  N.  C,  through  Longshoals,  N.  C..-1 
and  about  4  miles  east  of  Lincolnton,  N.  C.  The  belt  reaches  its 
maximum  width  of  2  miles  not  far  south  of  the  northern  border  oi! 
Gaston  County,  N.  C.  If  these  localities  be  noted  upon  the  map,  hi 
is  seen  that  the  belt  extends  about  northeast  from  Gaffney  to  a  little 
