242  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1906,   PART    I. 
sample  taken  across  50  feet  of  this  formation  was  analyzed  by  A.  J. 
Phillips  with  the  following  result: 
Analysis  of  Minnehahta  rum  stone. 
Silica  (Si02) 10.52 
Alumina  (A1203) 46 
Ferric  oxide  (Fe._>0:i) L.  55 
Manganese  oxide  (MnO) .  It 
Lime  (CaO) 43.30 
Magnesia  (MgO) 3.  53 
Sulphuric  anhydride  (S03) 06 
,n    ,-     f(Na.O) 05 
^lkaheS{(K20) 70 
Water  at  100°  C 50 
Ignition  loss 39.  22 
100.03 
This  limestone,  having  a  high  silica  content  and  a  comparatively 
low  sum  of  alumina  and  ferric  oxide,  is  much  poorer  in  quality  than 
the  Niobrara;  otherwise  it  is  fairly  good,  containing  low  sulphur 
and  not  prohibitively  high  magnesia.  Better  analyses  of  particular 
beds  of  the  Minnekahta  limestone  have  been  obtained  by  private 
parties. 
SHALE 
Graneros  shale.— At  the  end  of  the  railroad  spur  at  Bradley  station 
140  feet  of  shale  is  exposed  in  a  trough  lying  between  the  Dakota 
sandstone  hogback  on  the  west  and  the  hogback  formed  by  the 
sandstone  lens  in  the  Graneros  formation  on  the  east.  The  upper 
25  feet  of  the  shale,  which  here  dips  N.  85  E.  at  an  angle  of  so  ,  is 
sandy  and  is  unlit  for  making  Portland  cement.  The  lower  115  feet, 
however,  is  a  dark-gray  shale,  slightly  plastic,  with  little  or  no  grifr 
A  few  ironstone  nodules  occur  in  the  shale,  hut  these  have  been 
included  in  the  sample  and  are  evidently  not  detrimental.  The  shale 
outcrops  for  three-eighths  of  a  mile  south  and  at  least  U  miles 
north  of  Bradley  spur.  It  is  soft  and  could  be  readily  quarried  by 
steam  shovel.  An  analysis  by  Mr.  A.  .1.  Phillips  of  a  sample  taken 
across  the  middle    10  feet  of  the  shale  follows: 
Analysis  of  Graneros  shale. 
Silica  (Si02) 63.60 
Alumina  (A1203) I  1.  <i<'. 
Ferric  oxide  (Fe203) 7.  It 
Manganese  oxide  (MnO) .20 
Lime  (CaO) ?s 
Magnesia  (MgO) .  16 
Sulphuric  anhydride  (S03) •">:'. 
\lk,li<J(Na20) :17 
Alkallesi(K20) L.79 
Water  al  100°  C 2. 86 
Ignition  loss 7.  6  1 
100. 33 
