280  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
Generalized  tabular  section  of  Algonkian  rocks  in  the  Coeur  d' Alene  district. 
No. 
2 
Name. 
Description. 
Striped    Peak     forma- 
tion. 
Wallace  formation 
St.  Regis  formation 
Revett  qnartzite 
Burke  formation 
Prichard  slate. 
Total 
Sandstones,  siliceous,  generally  flaggy 
to  shaly;  colors  mostly  green  and 
purple;  characterized  by  shallow- 
water  features,  as  ripple  marks,  sun 
cracks,  etc. 
Thin-bedded  sandy  shales,  underlain  by 
rapidly  alternating  thin  beds  of  ar- 
gillite,  calcareous  sandstone,  impure 
limestone,  and  indurated  calcareous 
shale;  these  underlain  in  turn  by 
green  siliceous  argillites.  Shallow- 
water  features  throughout.  Slaty 
cleavage  common. 
Sandstones,  generally  flaggy  or  shaly; 
usually  fine-grained  and  much  indu- 
rated; colors  mostly  green  and  pur- 
ple; characterized  by  shallow-water 
features. 
White  quartzites,  generally  rather 
thick-bedded;  interstratified  with 
subordinate  quantities  of  micaceous 
sandstone. 
Gray,  flaggy,  fine-grained  sandstones 
and  shales,  with  interbedded  purple 
quartzitic  sandstone  (the  proportion 
varies  widely  in  different  parts  of  the 
district)  and  white  quartzite.  The 
formation  characterized  throughout 
by  shallow- water  features. 
Mostly  blue-black,  blue-gray  to  light 
gray  slates,  generally  distinctly  band- 
ed. Considerable  interbedded  gray 
sandstone.  Upper  portion  character- 
ized by  rapid  alternations  of  argil- 
laceous and  arenaceous  layers,  and 
by  shallow- water  features.  Base  not 
exposed. 
Thickness. 
Feet. 
1,000+ 
2,500=b 
800: 
1,000: 
1,700: 
8,000: 
15, 000 
The  Prichard  slate  is  the  thickest  and  the  most  homogeneous  of  thcJI f 
formations  in  the  Coeur  d'Alene  district  and  occupies  the  greatest 
area.  It  is  also  one  of  the  most  distinctive,  the  regularly  banded  i 
bluish-gray  slates  being  readily  recognized.  It  can  be  distinguished 
from  certain  somewhat  similar  beds  in  the  Wallace  formation  by  its 
noncalcareous  character  and  by  the  fact  that  it  weathers  in  reddish- 
brown  tints,  while  the  weathered  exposures  of  the  Wallace  formatioj 
are  yellowish  gray.  Slaty  cleavage  is  usually  fairly  well  developed 
and  of  a  more  regular  character  than  in  the  younger  formations  oJ 
the  district.  It  rarely  obscures  the  bedding,  to  which  it  is  usuallij 
inclined  at  considerable  angles.     In  some  places  cleavage  and  bedding 
