AREA   NORTH   AND    NORTHEAST   OF    LAKE    HURON.  417 
Very  numerous  details  are  given,  which  can  not  be  summarized. 
Williams,32  in  1891,  gives  microscopical  notes  on  various  rocks 
from  the  Sudbury  district.  The  sedimentary  rocks  are  found  to  in- 
clude those  which  are  plainly  clastic,  those  which  are  clastic  but 
partially  recrystallized,  and  those  which  are  highly  crystalline  but 
probably  derived  from  elastics.  In  the  last  division  are  placed 
felsite,  gneiss  conglomerate,  and  gneiss.  The  eruptives,  including 
various  acidic  and  basic  deep-seated  and  surface  rocks,  also  show 
extensive  metamorphism  and  recrystallization.  Placed  among  the 
highly  crystalline  rock,  probably  derived  from  the  elastics,  are  cer- 
tain felsites,  gneiss  conglomerates,  and  gneisses.  Certain  granites, 
gneisses,  and  schists  are  of  uncertain  origin,  but  give  no  indication 
of  clastic  derivation. 
Bell,33  in  1892,  gives  a  general  account  of  the  Laurentian  and  Hu- 
ronian  systems,  and  a  sketch  of  the  geology  of  the  country  extending 
from  Lake  Huron  northward  to  Lake  Temiscaming  and  from  Lake 
Ni  pissing  westward  to  Spanish  River.  The  Laurentian  system  is 
divided  into  an  upper  and  a  lower  formation.  The  latter  consists  al- 
most entirely  of  fundamental  gneiss,  while  the  upper  Laurentian  ap- 
pears to  consist  of  metamorphosed  and  sedimentary  strata,  to  some 
extent,  at  least. 
The  lower » division  of  the  Laurentian  consists  of  red  and  gray 
gneiss,  usually  much  bent  or  disturbed,  and  having  generally  a  rudely 
foliated  structure  and  a  solid  or  massive  character.  The  feldspar  is 
almost  entirely  orthoclase.  The  upper  division  of  the  Laurentian  is 
more  complex.  It  possesses  more  regularity  in  stratification  and  in- 
cludes great  banded  masses  of  crystalline  limestones,  vitreous  quartz- 
ites,  mica  schist  and  hornblende  schist,  massive  pyroxene,  and  massive 
and  foliated  labradorite  rocks.  Considerable  areas  of  granite  and 
syenite  occur  in  the  formation.  The  Upper  Laurentian  of  the  Ottawa 
Valley  may  be  roughly  estimated  at  50,000  to  100,000  feet  in  thickness. 
While  the  older  Laurentian  rocks  afford  no  proof  of  the  permanent 
existence  of  the  sea  upon  the  earth,  water  appears  to  have  been  pres- 
ent, perhaps  only  as  precipitations  upon  the  surface,  at  every  stage  of 
its  formation.  But  the  deposits  of  limestone  and  tolerably  pure  silica 
in  distinct  bands  in  the  Upper  Laurentian  afford  strong  support  to 
the  aqueous  theory  of  its  deposition. 
With  the  beginning  of  the  Huron ian  period  great  volcanic  activity 
began,  and  there  is  evidence  of  the  permanent  abode  of  water  on  the 
surface  of  the  earth.  The  general  character  of  the  Huronian  rocks 
may  be  said  to  be  pyroclastic,  by  this  signifying  that,  although  frag- 
mental,  they  have  nevertheless  had  an  igneous  origin. 
The  area  mapped  between  the  Huronian  belt  and  the  shore  of 
Georgian  Bay  appears  to  belong  to  the  Upper  Laurentian.    The  rocks 
55721— Bull.  360—09 27 
