HESS    AND 
GRATON. 
OCCURRENCE    AND    DISTRIBUTION    OF    TIN.  167 
8,000  feet,  from  which  the}^  gradually  lower,  northward,  to  half  that 
height. 
The  granites  become  porphyritic  in  the  main  range,  often  contain- 
ing much  tourmaline  in  the  tin  regions,  where  they  sometimes  lose 
their  mica  content.  The  rocks  are  deeply  weathered,  and  the  valleys 
are  filled  with  their  detritus.  Through  this  detritus  cassiterite  is 
scattered,  forming  the  placers  from  which  most  of  the  tin  of  the 
region  is  obtained. 
Of  the  sedimentary  rocks,  the  limestone  is  the  most  abundant  and 
important,  and  in  it  deep  holes,  formed  by  weathering,  sometimes 
contain  rich  accumulations  of  stream  tin. 
Quartzose  and  feldspathic  dikes,  carrying  cassiterite,  cut  the  gran- 
ite at  many  places.  Cassiterite  occurs  in  the  granite  as  impregna- 
;ions,  veins,  and  stockworks.  The  veins  are  found  also  in  the  lime- 
stone and  sandstone. 
On  the  east  side  of  the  range  veins  occurring  in  slate  are  being 
vorked.  They  vary  greatly  in  thickness,  generally  have  indistinct 
vails,  and  the  cassiterite  impregnates  the  country  rock.  This  de- 
posit is  four  days  by  boat  up  a  river  from  Kuantan,  a  small  town  on 
he  east  coast,  225  miles  by  steamer  from  Singapore. 
The  minerals  accompanying  cassiterite  in  the  various  veins  are 
ourmaline,   topaz,   fluorite,   wolframite,   iron    pyrites,   chalcopyrite, 
rsenopyrite,  bornite^  scheelite,  sapphire,  magnetite,  and  rhodochro- 
ite,   besides   the   usual    minerals   of    the   inclosing    rocks.      Small 
mounts  of  thorium  and  cerium  minerals  have  also  been  found  in 
ome  places.     All  of  these  minerals,  except  those  destroyed  by  weath- 
ring,  as  the  sulphides,  are  also  found  in  the  placers. 
The  largest  placers  of  the  Malay  States  are,  on  the  western  side, 
ut  fields   are   also   worked  on  the   eastern   side.     They   have   been 
worked  for  hundreds  of  years  and  are  now  producing  over  C>0  per 
ent  of  the  tin  that  finds  its  way  into  the  general  commerce  of  the 
rorld.     The   Kinta   district,   in   the   State   of   Perak,   contains   the 
ichest  and  most  extensive  placers  of  the  region.     The  placers  ex- 
ind  from  the  hillsides  out  into  the  plain,  being  residual   upon  the 
ill   slopes   and   largely    alluvial   below.     The   hillside   placers   are 
ften  richer  and  contain  larger  pieces  of  tin  ore,  but  are  shallower. 
'he  richest  ground  is  just  at  the  foot  of  the  hills.     The  cassiterite 
ay  be  distributed  throughout  the  gravel,  but  is  generally  in  the 
>wer  part  and   is  covered  by   an  overburden  of   barren   alluvium 
om  10  to  40  feet  or  more  in  thickness.     The  pay  gravel  may  be 
any  thickness  up  to  over  140  feet,  which  it  reaches  at  one  place  in 
erak. 
Nearly  all  work  is  done  by  Chinese  laborers,  and  many  of  the 
acers   are   controlled   by   them.     The   overburden   is   removed    by 
