554  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         r bull.  260. 
Feet. 
Sandstone 150 
Coal    (No.   3) 5i 
Clay    (No.   3) 24 
Coal    (No.   4) S 
Sandstone    (white) 70 
Clay    (No.  4) 12 
Sandstone 150 
Coal    (No.   5) 4 
Flint  clay    (No.  5) 7 
Sandstone 
The  beds  of  coal  are  all  workable  and  are  of  good  quality.  None 
of  the  coal  that  is  mined  is  sold,  but  all  is  used  in  burning  the  clay. 
Of  the  clay  beds  only  Nos.  1  and  2  are  being  worked  at  the  present 
time.  No.  1  clay  is  fine  grained,  massive,  and  when  broken  shows 
sharp  edges  and  an  uneven  fracture.  No.  2  clay  is  almost  black  and 
breaks  with  a  conchoidal  fracture.  It  is  heavy,  massive,  and  com- 
pact. No.  3  clay  is  dark,  almost  black,  and  contains  a  little  bitumi- 
nous matter.  It  is  hard,  compact,  and  heavy.  No.  4  clay  is  dark 
gray,  massive,  and  breaks  irregularly.  It  is  more  plastic  than  the 
associated  clays.  The  major  portion  of  the  clay  that  is  mined  is  used 
at  the  plant  near  by  in  the  manufacture  of  vitrified  bricks,  but  a 
portion  of  it  is  shipped  to  Van  Asselt. 
Among  the  coal-bearing  strata  in  the  vicinity  of  Renton  are  beds 
of  shale  which  are  of  value,  and  one  of  these  has  been  developed  by 
the  Renton  Clay  Company.  The  bed  of  clay  which  is  used  is  about 
25  feet  thick  and  lies  very  nearly  flat..  It  outcrops  upon  a  hillside, 
and,  since  only  a  little  stripping  is  necessary,  the  clay  is  obtained  by 
quarrying  rather  than  b}^  the  usual  mining  methods. 
Along  Duwamish  River,  south  of  Seattle,  are  a  number  of  clay 
deposits,  which  have  been  utilized  chiefly  in  the  manufacture  of  com- 
mon and  hollow  brick  and  draintile.  Some  of  the  clay  beds  contain 
marine  shells,  indicating  a  slight  rise  within  comparatively  recent 
times.  As  far  as  observed,  the  maximum  height  of  the  clay  beds 
above  tide  is  about  50  feet.  Except  for  the  oxidized  portions  which 
make  up  the  first  10  or  15  feet  of  the  clay,  the  remainder  of  it  is  of  a 
deep  bluish  color,  usually  fine  grained  and  plastic,  but  now  and  then 
containing  thin  lenses  of  sand  and  occasionally  small  pebbles.  While 
it  contains  sufficient  fluxes  to  give  it  a  fairly  low  melting  point,  it 
makes  a  common  brick  of  extraordinary  hardness  and  strength. 
At  other  places  in  the  vicinity  of  Seattle  are  clays  of  glacial  origin 
having  great  extent.  The  glacial  sediments  about  Puget  Sound  are  as 
a  rule  very  thick.  With  the  beds  of  till,  stratified  sands,  and  gravel 
are  occasional  layers  of  clay,  which  are  of  value  for  the  making  of 
common  brick.     The  clay  is  usually  bluish  and  comparatively  free 
