196  PRE-CAMBRTAN    GEOLOGY    OF    NORTH    AMERICA. 
general  nearly  flat  lying,  and  the  formation  has  a  much  younger 
aspect  than  the  other  two  quartzite  formations  in  the  region. 
For  fuller  summaries  of  articles  referring  to  the  Wisconsin  ore- 
bearing  districts  see  Monographs  V,  XIX,  and  XLVI  of  the  United 
States  Geological  Survey. 
SECTION  3.     MINNESOTA. 
SUMMARY  OF  LITERATURE. 
Catlin,130  in  1840,  finds  the  red  pipestone  quarries  of  the  Coteau 
des  Prairies  to  consist  of  a  perfectly  stratified  rock  in  layers  of  light- 
gray  and  rose-  or  flesh-colored  quartz,  the  deposit  being  evidently 
sedimentary  and  of  secondary  age. 
Norwood,131  in  1847,  describes  various  rocks  on  St.  Louis  River  in 
the  district  between  Fond  du  Lac  and  the  Falls  of  St.  Anthony,  and 
from  the  mouth  of  Montreal  River  to  the  headwaters  of  Wisconsin 
River  by  way  of  Lake  Flambeau.  On  St.  Louis  River  a  conglom- 
erate is  found  to  rest  unconformably  upon  the  lower  slates,  the  junc- 
tion of  the  slates  and  conglomerates  being  exposed. 
Norwood,132  in  1852,  gives  a  great  number  of  details  as  to  the 
geology  of  middle  and  western  Minnesota  and  the  country  adjacent  to 
the  southwest  shore  of  Lake  Superior,  illustrating  the  relations  of  the 
shales,  trap  rocks,  granites,  etc.,  and  showing  the  manner  of  intrusion 
of  the  eruptives  and  the  complicated  folding  to  which  the  strata  have 
been  subjected.  At  St.  Louis  and  Black  rivers  the  sandstone  rests 
unconformably  upon  the  underlying  argillaceous  and  siliceous  slates. 
Eames,133  in  1866,  mentions  different  crystalline  rocks  as  occurring 
at  many  points  in  northeastern  Minnesota. 
Eames,134  in  1866,  describes  in  Minnesota  various  granitic,  igneous, 
and  metamorphic  rocks.  The  most  prevalent  rocks  found  in  the 
northern  part  of  the  State  are  granite,  porphyry,  hornblende  slates, 
siliceous  slates,  trap,  greenstone,  talcose  slate,  primitive  schistose  rock, 
gneiss,  and  Potsdam  sandstone.  The  rocks  of  the  upper  Mississippi 
River  are  described.  At  Pokegama  Falls  the  rock  is  a  quartzite  be- 
longing to  the  Potsdam.  There  is  also  found  along. the  river  jasper- 
oid  rock  with  iron  ore  and  argillaceous  slate.  In  Stearns  County  are 
numerous  exposures  of  granite.  The  varieties  of  rocks  in  the  Ver- 
milion Lake  district  are  found  to  be  very  numerous. 
Hall  (James),135  in  1869,  finds  in  the  vicinity  of  New  Ulm,  on  Big 
Cottonwood  River  and  on  the  Little  Cottonwood,  extensive  exposures 
of  quartzite.  At  New  Ulm  the  rock  is  shown  to  be  a  metamorphosed 
quartz  rock  or  conglomerate.  This  rock  is  succeeded  below  by  com- 
pact quartz  rock,  with  beds  of  syenite,  which  graduate  still  lower  into 
purple  or  reddish  quartz  rock  in  distinct  layers,  alternating  with 
shaly  seams.    The  quartzite  of  this  region  has  a  thickness  of  not  less 
