192  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
At  various  places  throughout  the  belt  these  dikes  carry  cassiterite, 
the  dioxide  of  tin.  Development  has  not  been  sufficient  to  allow  any 
extended  generalizations  as  to  the  occurrence  of  the  tin,  but  certain 
facts  have  been  learned  and  may  be  briefly  presented.  The  cassiterite 
is  very  unevenly  distributed  throughout  the  rock.  In  general  it  is 
concentrated  along  certain  lines,  usually  steeply  pitching  in  the  dike 
and  constituting  ore  shoots.  These  ore  shoots  are  in  general  even 
more  irregular  than  the  dikes,  and  pinch,  swell,  branch,  give  out  and 
come  in  again  in  a  most  erratic  manner.  Some  of  the  ore  bodies, 
however,  have  a  considerable  extent  in  two  dimensions,  and  in  certain 
cases  persist  as  far  as  present  explorations  have  gone.  The  cassiterite 
is  crystalline,  but  only  rarely  has  good  crystal  faces.  In  a  few  cases 
well-formed  crystals  have  been  found.  It  occurs  from  minute  grains 
up  to  individuals  weighing  as  much  as  2  pounds,  and  aggregates 
which  are  almost  entirely  cassiterite  sometimes  weigh  several  hundred 
pounds.  The  mineral  is  usually  dark  brown  to  almost  black,  and  has 
a  metallic  luster.  In  a  few  instances  it  has  been  found  of  lighter 
color.  It  is  very  friable,  and  in  consequence  often  appears  to  be  low; 
in  the  scale  of  hardness. 
Wolframite  has  been  reported  as  an  accompaniment  of  the  cassiter-  - 
ite,  but  careful  search  has  failed  to  reveal  its  presence.  A  veinlet: 
about  2  millimeters  wide  carrying  fluorite  cuts  the  pegmatite  at  the 
Faries  mine  south  of  Kings  Mountain.  There  also  occur  at  that  mine 
small  masses  of  a  brownish-purple  mineral,  which  proves  to  be  a 
phosphate  of  manganese  and  Avhich  is  apparently  of  later  origin  than 
the  tin.  No  minerals  other  than  cassiterite  and  those  above  men- 
tioned have  yet  been  found  in  the  pegmatite. 
Granitic  dikes  older  than  the  pegmatite  and  closely  associated  with 
it  carry  tourmaline;  and  quartz  vein  of  uncertain  relative  age.  aiso 
rich  in  tourmaline,  likewise  occur  near  the  pegmatite  dikes.  While 
there  may  be  a  genetic  connection  between  the  pegmatite  dikes  and 
the  larger  masses  of  granite  which  occur  nearby,  no  such  relation  has 
thus  far  been  established. 
Careful  examination  of  the  wall  rock  of  the  pegmatite  dikes,  both 
by  crushing  and  panning  and  under  the  microscope,  indicates  that 
the  tin  mineral  is  confined  to  the  pegmatite  itself.  No  difference  in 
the  character  of  the  pegmatite  can  be  seen  where  cassiterite  is  abun- 
dant and  where  there  is  none. 
From  all  obtainable  evidence  it  seems  probable  that  the  cassiterite 
is  an  original  or  primary  constituent  of  the  pegmatite,  existing  us 
an  accessory  mineral,  like  magnetite  in  granite.  Some  factor  as 
yet  unknown  has  caused  the  segregation  or  concentration  of  the  tir 
in  certain  places. 
