panhise.]  LAKE    SUPERIOR    REGION.  119 
SECTION  V.   WORK  OF   THE  MINNESOTA  GEOLOGISTS  AND  ASSOCIATES. 
Eames,149  in  1866,  mentions  different  crystalline  rocks  as  occurring 
at  many  points  in  northeastern  Minnesota. 
Eames,150  in  1866,  describes  in  Minnesota  various  granitic,  igneous, 
and  metamorphic  rocks.  The  most  prevalent  rocks  found  in  the  north- 
ern 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  belonging  to  the 
Potsdam.  There  is  also  found  along  the  river  jasperoid  rock  with  iron 
Dre  and  argillaceous  slate.  In  Stearns  county  are  numerous  exposures 
jf  granite.  The  varieties  of  rocks  in  the  Vermilion  lake  district  are 
found  to  be  very  numerous. 
Hall  (James),151  in  1869,  finds  in  the  vicinity  of  New  IJlm,  on  the  Big 
Dottonwood  river  and.  on  the  Little  Cottonwood,  extensive  exposures 
)f  quartzite.  At  New  Ulm  the  rock  is  shown  to  be  a  metamorphosed 
piartz  rock  or  conglomerate.  This  rock  is  succeeded  below  by  com- 
3act  quartz  rock,  with  beds  of  syenite,  which  graduate  still  lower  into 
mrple  or  reddish  quartz  rock  in  distinct  layers,  alternating  with  shaly 
>eains.  The  quartzite  of  this  region  has  a  thickness  of  not  less  than 
L,500  feet.  At  Redwood  falls  are  found  gneiss  and  granitic  rocks  of 
Laurentian  age.  The  quartzites  are  regarded  as  of  the  age  of  the 
Euronian  of  Canada  and  equivalent  to  the  quartzites  of  Wisconsin. 
White,152  in  1870,  describes  the  quartzites  of  Iowa,  Minnesota,  and 
Dakota.  They  are  completely  metamorphosed,  intensely  hard  rocks, 
ilthough  the  lines  of  stratification  are  distinct  and  there  are  frequently 
seen  distinct  ripple  marks  upon  the  bedded  surfaces.  Not  infre- 
quently the  quartzite  is  conglomeratic.  In  them  no  fossils  have  been 
bund.  They  are,  however,  regarded  as  belonging  to  the  Azoic  age  be- 
cause of  their  complete  metamorphic  character,  because  of  their  dis- 
turbed condition,  and  because  the  Lower  Magnesian  limestone  at  New 
[Jim  rests-upon  the  quartzites  unconformably,  and  in  this  part  of  Noi  I  h 
America  no  disturbances  are  known  to  have  occurred  between  the  com- 
nencement  and  close  of  Paleozoic  time. 
Winchell  (N,  H),153  in  1873,  states  that  the  granitic  and  nieta- 
norphic  rocks  occupy  a  great  portion  of  the  state  of  Minnesota 
Fhese  are  regarded  as  Laurentian  and  Huronian.  Their  lithological 
md  mineralogical  characters  are  complex  and  variable.  The  original 
mcleus  was  granite  and  syenite,  and  around  these  are  arranged  the 
netamorphosed  slates,  and  gneisses  in  upturned  or  even  vertical  beds, 
addle  intercalated  with  them  are  numerous  injected  beds  or  dikes  of 
:rap.  The  Sioux  quartzite  and  those  of  New  Ulm  are  placed  as  a  purl 
)f  the  Potsdam  sandstone.  The  Potsdam  was  laid  down  before  the 
3lose  of  the  volcanic  disturbance,  for  the  St.  Croix  beds  of  later  age 
rest  unconformably  upon  the  Laurentian  as  well  as  upon  the  upturned 
