RANSOME.] 
COEUR    d'aLENE    DISTRICT,  IDAHO. 
279 
tinct  formations  is  difficult.  Sands  and  silts  accumulated  on  the 
subsiding  bottom  of  a  shallow  sea  to  a  thickness  of  over  10,000  feet. 
So  shallow  was  this  sea  that  most  of  the  sediments  retain  the  marks 
of  pre-Cambrian  ripples  and  were  occasionally  laid  bare  and  cracked 
by  the  sun.  Throughout  the  entire  period  of  deposition  there  was 
no  abrupt  change  in  the  general  character  of  the  sediments.     Muddy 
lomiles 
Sla-tes,qti.artz.ites,impuj-e       Syenite  and  Lodes  Mines 
b  me  stones,  and  sandstones     monxonite 
probably  of -Algjonluan  age 
FtfJ.  17. — Preliminary  ueolo;;ie  map  of  the  Coeur  d'Alene  district. 
silts  graded  into  sands  and  these  again  into  silts.  Under  such  cir- 
cumstances the  formations  recognized  in  the  following  table  have 
nore  or  less  arbitrary  upper  and  lower  limits.  The  typical  dark 
late  of  the  Pricharcl  formation  is  very  different  from  the  sericitic 
niartzite  of  the  Burke  formation,  but  the  two  are  connected  by  beds 
)f  intermediate  character.  In  the  accompanying  tabular  section 
:he  formations  are  arranged  from  the  bottom  upward  in  the  order 
>i  their  deposition: 
