342  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
Type  II. — Originating  in  the  replacement  by  iron  carbonate  of  a 
steeply  dipping  bed  of  limestone  along  the  contact  of  the  Stockbridge 
limestone  and  Hudson  schist.     Amenta  mines,  National  mine. 
Type  III. — Originating  in  the  replacement  by  iron  carbonate  of  a 
steeply  dipping  bed  of  limestone  entirely  within  the  Stockbridge 
limestone  series.     Leet  mines. 
Type  IV. — Originating  by  direct  deposition,  probably  as  limonite, 
in  a  basin  on  or  a  cavity  or  cavern  in  a  flat-lying  limestone.  Davis 
mines. 
The  original  iron  carbonate  was  undoubtedly  deposited  from  solu- 
tion as  a  replacement  of  a  limestone  and  not  deposited  in  a  basin 
contemporaneously  with  the  inclosing  rocks.  .  To  this  extent  the 
writer's  explanation  differs  from  that  offered  by  Dana  and  certain 
other  geologists.  On  the  other  hand,  it  is  clear  that  the  iron-bearing 
solutions  did  not  pass  freely  everywhere  through  a  mass  of  generally 
porous  rock  as  seems  to  be  required  by  the  commonly  accepted 
theoiy.  In  such  a  thoroughly  porous  mass  bedding  planes  could  not 
affect  the  shape  of  the  deposit,  the  only  restraining  influence  being 
the  "  impervious  pitching  trough,"  whose  existence  is  so  freely  pos- 
tulated and  in  the  New  York-New  England  district  so  rarely  proved. 
The  presence  of  bedded  iron  carbonate  in  depth  supports  the  ideas 
advanced  by  Catlett,  McCallie,  and  Hayes  as  opposed  to  the  theory 
that  the  limonite  deposits  are  always  entirely  superficial,  ceasing 
as  soon  as  bed  rock  is  reached. 
