CLAYS  AND  FULLER'S  EARTH. 
The  clays  of  eastern  United  States  were  discussed  in  a  professional 
paper  issued  by  the  United  States  Geological  Survey  during  the  last 
year.  Owing  to  its  comprehensive  character,  no  abstract  of  this 
important  work  has  been  attempted  for  the  present  publication.  The 
results  of  recent  field  work  by  the  Survey  on  the  clays  of  western 
Pennsylvania  are  given  in  the  following  paper. 
CLAYS  OF  THE  OHIO  VALLEY  IN  PENNSYLVANIA. 
By  L.  H.  Woolsey. 
INTRODUCTION. 
A  preliminary  report  on  the  clay  resources  and  industries  of  this 
region  is  here  presented  as  a  result  of  the  field  work  on  the  Beaver 
quadrangle,  Pennsylvania.  The  clay  industries  of  this  region  are  at 
present  practically  confined  to  the  valleys  of  Ohio  and  Beaver  rivers 
in  Beaver  County,  and  this  report  is  intended  to  treat  only  of  this  area, 
but  for  purposes  of  comparison  analyses  and  notes  of  clays  of  other 
districts  have  been  included. 
NATURE  OF  CLAY. 
Definition. — Popularly  clay  is  the  familiar  gritless  plastic  earth 
which  is  readily  molded  when  wet  and  which  retains  its  shape  on  dry- 
ing. To  the  manufacturer  clay  means  the  material  he  molds  and 
bakes,  and  this  may  correspond  to  the  above  or  to  any  mixture,  nat- 
ural or  artificial.  Technically  clay  is  Al2032Si022H20  plus  sand, 
plus  accessories.  Al2032Si022H20  is  pure  kaolin  or  kaolinite,  and 
the  sand  is  composed  of  grains  of  quartz  and  other  minerals.  The 
silica,  therefore,  occurs  chemically  combined  in  kaolinite  and  other 
minerals  and  also  in  the  free  state,  as  quartz  sand.  The  chief  acces- 
sories are  iron  oxide,  lime,  and  magnesia,  with  potash  and  soda  in 
smaller  quantities. 
Origin.—  Clay  originates  from  the  disintegration  of  rocks  containing 
minerals  made  up  largely  of  alumina  and  silica.     The  most  abundant 
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