3()4  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART   I. 
phase  of  treatment  on  account  of  the  expense  of  installing  washeraj 
for  the  price  of  sand,  and  often  its  use  or  rejection,  is  affected  by  the 
small  percentage  of  impurity  that  may  be  washed  away.  Tw  o  methl 
ods  of  washing  arc  followed.  One  method  involves  several  sets  of 
bins,  into  which  sand  and  water  are  elevated  or  pumped  so  that  the 
sand  settles  quickly  while  the  liner  impurities  are  washed  awa}^;  the 
other  employs  a  crude,  open-top  pug  mill,  in  which  rotating  u  augers'! 
or  screws  move  the  sand  up  inclined  troughs,  rolling  it  over  and  over 
so  that  by  attrition  it  is  freed  from  a  large  portion  of  its  impurities  and 
stain,  and  the  impurities  are  then  readily  removed  by  a  stream  of 
i  playing  down  the  troughs. 
Drying  iseffected  bythree  general  types  of  apparatus:  (1)  Rotary 
cylinders,  through  which  the  sand  passes  against  a  draft  of  flame  and 
hot  gas;  (2)  a  stationary  roaster,  and  (3)  coils  of  steam  pipes.  The! 
first  method  involves  the  greatest  initial  cost,  bul  i>  by  far  the  most 
rapid  and  efficient.  Fuller  description  of  methods  of  obtaining  and 
preparing  -and  will  be  found  under  the  heading  u  Detailed  descripl  ions 
of  sand  properties/5  pp.  :ir>7  :\7~). 
Sand  thai  passes  a  60-mesb  >i»  ve  or  one  of  smaller  mesh  is  regarded 
as  fine  grained;  that  which  passes  30-  and  L0-mesh  sieves  is  regardel 
a-  medium  grained,  and  that  winch  i>  retained  by  .'Hi-  or  20-mesl 
sieves  or  sieves  of  coarser  mesh  is  considered  coarse  grained.  These 
divisions  have  been  mad;'  the  basis  for  classifying,  according  to  their 
grain,  the   various  -and-  mentioned   in  the  following  notes. 
ROCKS    UTILIZED. 
INDIANA     \\l>    KENTUCKY. 
In  Indiana  sandstones  of  Silurian,  Devonian,  Carboniferous,  and 
Tertiary  age  have  been  utilized  for  glass  making,  hut  at  present  the 
Carboniferous  sandstone  furnishes  the  greater  part  of  the  glass-sand 
out  put . 
Silurian.  Rocks  of  Niagara  age  extend  from  the  Illinois  line,  in 
New  tmi  County,  eastward  nearly  across  Indiana  and  cover  the  upper 
Wabash  Valley.  For  the  most  part  they  are  buried  under  a  greai 
thickness  of  drift.  These  Niagara  rocks  consist  principally  of  magj 
nesian  limestone  of  varying  composition  and  texture,  but  in  some  local- 
ities they  occur  as  thin  lenses  of  -andstone.  One  of  these  lenses, 
near  Kenneth,  Cass  County,  3  miles  west  of  Logansport,  is  5J  feet] 
thick  and  is  composed  of  pure  white  quartz  sand,  containing  only 
traces  of  calcium  carbonate  and  iron.  Just  west  of  the  Hamilton- 
Madison  county  line,  at  a  point  \\  miles  southwest  of  Fishersburg, 
a  5-foot  bed  of  very  pure  white  sandstone  has  been  quarried  for  glasi 
making.  At  this  point  the  rock  is  massive,  fine  grained,  and  friable] 
and  is  overlain  by  less  than  1  foot  of  bull"  magnesian  limestone,  over 
