464  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
Two  methods  of  drying  sand  are  in  common  use  the  rapid  method,  effected  by  nieai 
of  rotary  cylindrical  dryers,  which  operate  on  a  principle  similar  to  that  applied  in  cemei 
mills,  and  the  slower  method  of  allowing  the  sand  to  settle  through  coils  of  steam  pipe 
In  the  rotary  driers  the  cylinder  is  slightly  inclined  to  the  horizontal;  damp  sand  is  fed  i 
at  the  higher  end  and,  aided  by  gravity,  moves  gradually  toward  the  lower  end  of  tl 
cylinder.  Heated  and  incandescenf  gases  are  forced  into  the  cylinder,  the  interior  of  whic 
maybe  fitted  with  an  angle  iron  that  lifts  and  drops  I  ie  sand  alternately,  thus  expo) 
ing  it  more  completely  to  the  action  of  heat.  There  is  some  objection  to  this  method  o 
the  ground  of  overheating  the  sand  and  the  consequent  danger  of  its  setting  lire  to  th 
bins,  [f  the  heat  is  properly  regulated,  or  if  bins  are  of  fireproof  material,  the  danger  i 
minimized,  and  since  drying  is  completed  in  from  live  to  ten  minutes  great  economy  of  tim 
is  effected— an  essential  feature  where  a  large  output  is  desired.  Fuller  discussion  c 
methods  of  obtaining  and  preparing  sand  will  be  found  in  the  descriptions  of  individus 
plants  under  the  head  "  Details  of  sand  properties,"  below. 
In  the  accompanying  tables  are  given  the  chemical  composition  and  physical  propertio 
of  twelve  sands  from  Arkansas,  Missouri,  Kansas,  and  Wisconsin.  These  sands  hav 
attracted  attention,  either  by  their  purity  and  general  fitness  or  by  their  proximity  b 
manufacturing  centers.  Direct  comparison  with  sands  of  proved  value  can  be  made  b 
reference  to  corresponding  tables  in  the  paper  "Requirements  of  sand  and  limestone  fc 
glass  making,"  page-   152-458  of  this  bulletin. 
DETAILS   OF   SAND    PROPERTIES. 
The  glass-sand  industry  in  Illinois  is  mainly  centralized  in  Lasalle  County,  along  lllinoi: 
and  box  rivers  near  their  junction.  Topographic  maps  of  Lasalle  and  Ottawa  quad 
rangles,  comprising  this  area,  are  issued  by  t  he  Sun  ey.  The  St .  Peter  sandstone,  which  if 
the  lock  utilized,  has  been  exposed  in  tlii-  area  as  the  remit  of  erosion  across  a  low  anti- 
clinal fold,  the  axis  of  which  passes  northwesl  and  southeast  about  2  miles  below  Utici 
The  lowest  rock  exposed  along  the  axis  of  this  fold  is  a  magnesian  limestone  containhn 
natural  cement-rock  beds.  It  lies  just  below  the  St.  Peter  sandstone  and  is  exposed  aloia 
Illinois  River  Vallej  for  about  :;  miles  below  Utica.  The  dips  on  the  west  limb  of  the 
anticline  are  very  marked  near  the  axis,  but  to  the  east  they  are  more  gentle,  and  in  both 
directions  the  dip  flattens  out  so  as  *to  bee.. me  imperceptible.  Illinois  River  flows  in  I 
broad,  flat,  rock-bottomed  valley  with  precipitous  sides,  and  below  the  rock  floor  of  the 
valley  the  stream  has  cut  its  present  chatfnel  from  20  to  30  feel  in  depth.  As  a  consequent 
of  the  steep  westward  dip,  which  occurs  about  II  miles  easi  of  Lasalle,  the  extent  of  the 
St.  Peter  sandstone  on  the  wesl  limb  of  the  anticline  is  limited  to  a  few  hundred  yards. 
Northward  beyond  the  river  valley  the  sandstone  forms  the  country  rock  over  several 
townships.  Eastward  from  Qtica  to  Ottawa  the  broad  Illinois  Valley  is  cut  in  the  flat- 
lying  sandstone,  as  is  the  narrowei  valley  of  Fox  River,  to  a  point  above  Wedron.  Lime- 
stones of  Carboniferous  and  occasionally  of  Trenton  aye  overlie  the  sandstone  along 
the  valley  bluffs.  Transportation  facilities  are  extremely  favorable,  since  two  railroads 
traverse  the  \  alley  at  ( )t  bawa,  and  this  advantage,  together  with  the  inexhaustible  quantiti 
of  very  pure  sand  easily  obtained,  has  brought  the  production  of  silica  into  prominence 
among  the  activities  of  the  Illinois  Valley. 
Ottawa. — The  Ottawa  Silica  Company's  property  lies  about  \l  miles  west  of  town,  near 
the  Illinois  and  Michigan  Canal.  This  company  operates  two  mills,  about  one-half  mill 
apart,  each  mill  deriving  sand  from  an  open  pit  sunk  below  the  level  of  the  \  alley  bottom. 
The  St.  Peter  sandstone  lies  horizontal  and  is  everywhere  near  the  surface  throughout  this 
portion  of  the  valley.  At  these  quarries  a  few  inches  to  3  feet  of  soil  and  glacial  debris 
have  been  scraped  away,  laying  bare  the  old  waterworn  and  potholed  surface  of  the  sandl 
stone.  At  the  sides  of  the  valley  the  formation  rises  30  to  50  feet  above  the  valley  floor,  and 
drilling  is  reported  to  have  shown  the  deposit  to  extend  280  feet  below  it,  so  that  its  total 
