190  PRE-CAMBRTAN    GEOLOGY   OF    NORTH    AMERICA. 
much   more   common  than  the   Huronian,   and   resemble  the   Huro-  j 
man  bedded  diorites.    It  is  suggested  that  these  dikes  have  afforded' 
the  material  for  the  greenstones  and  related  schists  of  the  Huronian. 
May  not  also  considerable  of  the  magnetite  come  from  the  same  s 
source  ? 
Wright,117  in  1880,  in  describing  the  western  and  southern  exten- 
sion 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  to  the  Lower  Huronian  is  an  open  question. 
Strong,  Sweet,  Brotherton,  and  Chamberlin,118  in  1882,  further 
describe  the  quartzites  of  Barren  and  Chippewa  counties.  They  are 
found  in  several  localities  to  contain  beds  of  conglomerate,  to  have 
not  infrequently  distinct  bedding,  and  to  contain  locally  beds  of  pipe- 
stone. 
King,119  in  1882,  describes  the  rocks  of  the  upp'er  Flambeau  Valley. 
They  are  found  to  be  mainly  granite,  gneiss,  hornblende  schist,  and 
mica  schist,  and  are  all  referred  to  the  Laurentian. 
Irving  and  Van  Hise,120  in  1882,  describe  the  crystalline  rocks  of 
the  Wisconsin  Valley.  The  crystalline  rocks  here  found  are  a  great 
series  of  schistose  gneisses.  Alternating  with  these  are  finer  grained 
and  more  highly  lamellar  schists.  Intersecting  the  gneiss  are  dikes 
of  various  basic  rocks,  while  structureless  masses  of  granite,  pre- 
sumably intrusive,  are  also  found.  In  the  vicinity  of  Wausau  are 
argillaceous  quartz  schists  and  quartzites,  which  on  lithological 
ground  may  be  referred  to  the  Huronian,  although  of  the  structural 
relations  of  these  rocks  with  the  Laurentian  gneisses  nothing  is 
known. 
Chamberlin,121  in  1883,  gives  a  .systematic  account  of  the  geology 
of  Wisconsin.  The  rocks  of  Laurentian  age  are  mainly  of  the  gran- 
itic type,  consisting  largely  of  granites,  gneisses,  syenites,  and  horn- 
blendic,  micaceous,  and  chloritic  schists,  with  allied  rocks.  These 
are  associated  with  igneous  diabase,  diorites,  and  similar  rocks. 
This  series  is  regarded  as  a  sedimentary  accumulation,  on  the  grounds 
(1)  of  foliation  and  stratification;  (2)  of  the  alternating  bands  of 
varying  chemical  constitution;  (3)  of  the  verging  of  one  kind  of 
rock  into  another  laterally;  and  (4)  of  the  presence  of  kinds  of  rocks 
not  known  to  be  produced  by  igneous  agencies.  The  thickness  of 
these  sediments  is  enormous.  An  estimate  of  30,000  feet  is  probably 
not  too  great. 
The  calcareous  and  carbonaceous  beds  of  the  Laurentian  of  Canada, 
as  well  as  the  Archean  limestones  and  iron-ore  beds  of  New  York, 
are  considered  to  be  Huronian  rather  than  Laurentian,  and  if  this  is 
so  there  is  present  in  the  Laurentian  no  positive  evidence  of  life, 
although  future  investigations  may  reveal  evidences  of  organic  be- 
