336  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY;  1901.        Lbui.l.  260. 
deposits — such  evidence  as  Hayes  lias  been  able  to  obtain  in  Alabama 
and  Georgia. 
The  brown  hematite  deposits  considered  in  the  present  paper  occur 
in  the  counties  of  Dutchess  and  Columbia,  N.  Y.,  Berkshire,  Mass., 
and  Litchfield,  Conn..  Similar  deposits  occur  north  of  this  district, 
in  Vermont,  while  south  of  it,  though  they  are  but  slightly  developed 
in  southern  New  York  and  New  Jersey,  the  limonite  deposits  become 
large  and  numerous  in  Pennsylvania,  Virginia,  Tennessee,  Georgia, 
and  Alabama. 
GEOLOGY  OF  THE  REGION. 
The  portion  of  New  York  and  New  England  in  which  the  browJ 
hematite  deposits  are  best  developed  is  underlain  by  a  series  of 
highly  metamorphosed  and  much  folded  rocks,  varying  from  pre-] 
Cambrian  to  late  Ordovician  in  age. 
Geologic  formations. — Four  geologic  formations  appear  in  the  area 
in  question  and  must  be  considered  in  any  adequate  discussion  of  the 
age  and  origin  of  the  iron  ores.     These  are — 
1.  Pre-Cambrian  gneisses. 
2.  Poughquag  quartzite   (Georgian  or  lower  Cambrian). 
3.  Stockbridge  limestone  (Cainbro-Ordovician). 
4.  Hudson  schists  and  shales  (Ordovician). 
Each  of  these  rock  series  will  be  briefly  described. 
The  pre-Cambrian  rocks  of  the  region  consist  mainly  of  gneisses, 
with  subordinate  amounts  of  schist.  They  constitute  the  bulk  of  the 
NeAV  York  and  New  Jersey  highlands,  extending  northeastward  into 
Connecticut  as  Dover  Mountain  and  being  represented  farther  north 
in  Connecticut  and  Massachusetts  by  a  range  of  mountains  east  of  the 
Canaan-Stockbridge-Pittsfield  valley. 
The  Poughquag  formation  immediately  overlies  the  pre-Cambrian 
gneisses.  It  is  a  quartzite  very  variable  in  thickness,  ranging  from 
10  to  150  feet  or  more,  but  very  constant  in  composition  and  appear- 
ance. 
The  Stockbridge  limestone  is  a  white  to  bluish,  often  notably 
crystalline,  limestone.  This  limestone  is  usually  highly  magnesiam 
though  it  rarely  carries  sufficient  magnesia  to  qualify  as  a  true  dolo- 
mite, and  contains  occasional  beds  entirely  free  from  magnesia.  Geo- 
logically the  Stockbridge  limestone  is  essentially  the  metamorphosed 
equivalent  of  the  Cambrian,  Calciferous,  and  Trenton  series  of  the 
Mohawk  and  Champlain  valleys. 
Overlying  the  Stockbridge  limestone  is  a  thick  series  of  mica 
schists,  corresponding  to  the  Hudson  shales  of  the  Hudson  River 
Valley,  and  gradually  becoming  less  metamorphic  toward  the  Avest.  -I 
Geologic  structure. — While  faulting  on  any  visible  scale  is  de- 
cidedly uncommon  in  this  region,  the  rocks  are  very  strongly  folded. 
