116  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
found  in  the  Laurentian,  its  rocks  always  being  much  metamorphoset 
and  often  so  much  as  to  destroy  all  traces  of  bedding.  Underlying  tin 
quartzite  at  Sturgeon  river  falls  is  a  schist-conglomerate  which  ha* 
numerous  pebbles  of  what  appear  to  be  granite  and  gneiss  from  tin 
adjacent  Laurentian.  In  the  Pine  and  Poplar  river  regions  is  founc 
conglomeratic  quartz-schist  containing  micaceous  iron  and  magnetite 
In  the  Commonwealth  section  are  included  quartz-schists  which  ar« 
conglomeratic,  containing  pebbles  of  white  quartz  and  jasper.  Ther* 
are  also  found  in  the  upper  beds  of  the  Huronian,  conglomeratic  mica 
ceous  quartz-schists.  At  various  places  granites  and  gneisses  overlh 
conformably  the  younger  Huronian  schists,  into  which  they  send  dikes 
As  the  evidence  of  bedding  is  rare,  it  is  possible  that  toward  the  enc 
of  the  Huronian  period  there  was  a  great  eruptive  overflow  of  these 
rocks.  Cutting  the  Laurentian  rocks  in  all  directions  are  dike-lik( 
masses  of  granite  and  greenstone.  The  abundant  greenstone  dikes  o 
the  Laurentian  are  much  more  common  than  in  the  Huronian,  anc 
resemble  the  Huronian  bedded  diorites.  It  is  suggested  that  thes< 
dikes  have  afforded  the  material  for  the  greenstones  and  related  schist* 
of  the  Huronian.  May  not  also  considerable  of  the  magnetite  come 
from  the  same  source  f 
Wright,141  in  1880,  in  describing  the  western  and  southern  extensioi 
of  the  Menominee  range,  states  there  can  be  no  doubt  that  the  granite 
is  younger  than  the  lower  Huronian.  This  latter  dips  under  the  former 
and  veins  of  the  former  penetrate  the  latter,  but  whether  it  belongs  t< 
the  lower  Huronian  is  an  open  question. 
Strong,  Sweet,  Brotherton  and  Chamberlin,142  in  1882,  furthe: 
describe  the  quartzites  of  Barron  and  Chippewa  counties.  They  an 
found  in  several  localities  to  contain  beds  of  conglomerate,  to  have  no 
infrequently  distinct  bedding,  and  to  contain  locally  beds  of  pipestone 
King,143  in  1882,  describes  the  rocks  of  the  upper  Flambeau  valley 
They  are  found  to  be  mainly  granite,  gneiss,  hornblende-schist  anc 
mica-schist,  and  are  all  referred  to  the  Laurentian. 
Irving  and  Van  Hise,144  in  1882,  describe  the  crystalline  rocks  o 
the  Wisconsin  valley.  The  crystalline  rocks  here  found  are  a  grea 
series  of  schistose  gneisses.  Alternating  with  these  are  finer  graineli 
and  more  highly  lamellar  schists.  Intersecting  the  gneiss  are  dike 
of  various  basic  rocks,  while  structureless  masses  of  granite,  presumi 
ably  intrusive,  are  also  found.  In  the  vicinity  of  Wausau  are  argilla 
ceous  quartz  schists  and  quartzites,  which  on  lithological  ground  maj 
be  referred  to  the  Huronian,  although  of  the  structural  relations  of  thesi 
rocks  with  the  Laurentian  gneisses  nothing  is  known. 
Chamberlin,145  in  1883,  gives  a  systematic  account  of  the  geology 
of  Wisconsin.  The  rocks  of  Laurentian  age  are  mainly  of  the  granitj 
type,  consisting  largely  of  granites,  gneisses,  syneites,  hornblendic 
micaceous,  and  chloritic  schists,  with  allied  rocks.  These  are  associate( 
with  igneous  diabase,  diorites,  and  similar  rocks.    This  series  is  re 
