AREA    NORTH   AND    NORTHEAST   OF   LAKE    HURON.  411 
Bell,25  in  1890,  states  that  stretching  from  Lake  Huron  to  Lake 
Temiscamang  is  the  greatest  area  of  Huronian  rocks  in  Canada. 
The  most  prevalent  rock  in  this  region  is  graywacke,  often  conglom- 
eratic. Another  rock  of  great  abundance  is  a  quartz  diorite.  These 
two  are  the  parent  rocks  of  the  Huronian.  The  quartzites  and  clay 
slates  are  but  phases  of  the  graywacke.  The  rocks  of  this  region 
show  three  ways  by  which  gneiss  may  be  formed — by  direct  conver- 
sion of  the  thin-bedded  or  slaty  varieties  of  graywacke,  by  alteration 
of  the  mixed  quartz  and  feldspar  rock  derived  from  other  varieties 
of  it,  and  by  alteration  of  the  modified  quartz  diorites.  The  dolo- 
mites are  of  a  concretionary  or  segregated  nature,  derived  from  the 
hornblende  and  augite  of  the  rocks  with  which  they  are  associated. 
During  the  process  of  conversion  from  graywacke  into  syenite,  strings 
and  veins  of  magnetite  have  formed. 
Winchell  (Alexander),26  in  1890,  gives  further  observations  on 
the  Original  Huronian  region.  Northwest  of  Echo  Lake  is  found  a 
series  of  argillites,  slates,  quartzites,  and  schists,  which  are  frequently 
conglomeratic  and  in  one  place  contain  outcrops  of  hematite.  These 
strata  have  a  nearly  vertical  attitude,  strike  nearly  east-west,  and 
resemble  the  Knife  Lake  series  and  Ogishki  conglomerates  of  Minne- 
sota. These  rocks  can  not  belong  to  the  same  system  as  the  quartz- 
ites, upper  slate  conglomerates,  and  limestone  of  the  Huronian,  which 
dip  at  an  angle  of  20°.  There  is  here  a  genuine  discordance  of  stratifi- 
cation, and  two  series,  not  one,  as  mapped  by  Logan.  The  lower 
system  is  the  formation  which  occurs  at  Gros  Cap,  Goulais  Bay,  and 
Dore  River,  which  was  identified  by  Logan  with  the  Huronian  of 
Lake  Huron.  The  author  is  convinced  also  of  their  identity  with  the 
vertical  strata  in  Minnesota  and  Canada  known  as  the  Keewatin 
system.  It  is  also  clear  that  these  gnarled,  green  pebble  slates  are 
the  prolongation  of  the  lower  slate  conglomerate  of  the  Thessalon 
Valley. 
Winchell  (Alexander),27  in  1891,  maintains  that  the  Original 
Huronian  is  divisible  into  two  unconformable  series,  the  break  oc- 
curring between  the  upper  and  lower  slate  conglomerates,  and  the 
intervening  limestone  belonging  with  the  upper  series.  The  descrip- 
tions of  this  region  by  Murray  indicate  that  near  Lake  Wahnapitae 
there  is  a  stratigraphic  unconformity  between  the  upper  and  lower 
divisions  of  the  Original  Huronian,  as  here  the  slate  conglomerates 
are  in  a  nearly  vertical  attitude,  while  the  newer  members  seldom 
have  an  inclination  greater  than  45°.  In  every  instance  in  which 
the  lower  slate  conglomerate  has  been  traced  by  Logan  or  Murray  to 
the  proximity  of  the  gneiss  these  formations  seem  to  be  conformable 
in  position,  though  the  actual  juxtaposition  was  concealed.  At  Mur- 
ray Hill  the  slate  conglomerate  has  a  dip  of  78°  S.,  while  2  miles 
south  of  this  it  has  a  dip  of  40°  S.  30°  W.     The  first  is  regarded  as 
