424  PKE-CAMBEIAN    GEOLOGY   OF    NORTH   AMERICA. 
to  the  overlying  Huronian  series.  However,  on  Lake  Temiscaming 
the  Laurentian  is  unconformably  below,  and  in  direct  contact  with, 
an  arkose  of  Huronian  age,  which  has  apparently  been  derived  from 
the  disintegration  of  the  Laurentian  granite. 
The  Huronian  occupies  about  a  third  of  the  combined  area  of  the 
two  sheets.  It  is  separable  into  three  divisions,  in  ascending  order  as 
follows:  (1)  Breccia  or  breccia  conglomerate,  (2)  graywacke  shale  or 
slate,  and  (3)  feldspathic  sandstone  or  quartzite.  The  maximum 
thickness  of  the  first  division  is  600  feet;  of  the  second,  100  feet;  and 
of  the  third,  1,100  feet.  Associated  with  these  clastic  rocks  are  va- 
rious rocks  of  igneous  origin,  including  deep-seated  diabase  and  gab- 
bro  and  volcanic  ejectamenta. 
Coleman,  in  1S99  and  1901,  discusses  the  general  geology  of  this 
region,  together  with  that  of  the  north  shore  of  Lake  Superior.  See 
summary  in  Chapter  III,  section  4,  Lake  Superior  region,  pages 
285-289. 
Miller,44  in  1901,  describes  the  iron  ores  and  associated  rocks  of  the 
area  adjacent  to  Lake  Temagami  and  of  the  Lake  Wahnapitae  and 
Hutton  areas  to  the  west,  all  in  the  Nipissing  district  of  Ontario. 
The  Temagami  area  has  been  previously  mapped  and  reported  upon 
by  A.  E.  Barlow.a  Miller's  discussion  of  the  general  geology  of  this 
area  follows  that  of  Barlow,  with  minor  additions  and  corrections. 
Miller,45  in  1902,  publishes  geological  notes  taken  on  a  canoe  trip 
from  Lake  Temiscaming  northward  to  the  Height  of  Land.  Special 
attention  was  paid  to  the  occurrence  of  minerals  of  commercial  value, 
and  no  mapping  is  attempted.  He  finds  various  kinds  of  igneous 
rocks,  both  plutonic  and  volcanic,  such  as  granite,  syenite,  diorite, 
olivine  diabase,  quartz  porphyry,  and  others  of  less  importance.  In 
addition  to  these  most  of  the  metamorphic  fragmental  rocks  charac- 
teristic of  the  Huronian  occur,  among  which  may  be  mentioned 
quartzite,  slate  graywacke,  and  different  varieties  of  the  pyroclastic 
series,  ash  rocks,  and  agglomerates.  The  popular  belief  that  the 
Height  of  Land  in  this  district  represents  the  highest  point  of  the 
surface  from  which  sediment  was  derived  for  the  formation  of  de- 
posits of  different  ages  which  lie  to  the  south  is  scarcely  based  on  fact. 
He  found  what  appear  to  be  thick  deposits  of  Huronian  conglomerate 
and  other  water-formed  material  resting  on  the  surface  close  to  the 
Height  of  Land.  It  is  evident  from  this  that  the  surface  level  must 
have  changed  considerably  since  Huronian  times,  and  that  what  is 
now, the  Height  of  Land  may  have  once  been  a  comparatively  low- 
lying  area. 
Van  Hise  and  Seaman,46  in  1902,  examined  the  contact  of  the 
series  of  slates  and  graywackes  called  by  Bell  Cambrian,  but  believed 
by  Van  Hise  and  Seaman  to  be  Upper  Huronian,  with  the  Laurentian 
"  Ann.  Rept.  Geol.  Survey  Canada,  vol.  10,  pt.  1,  for  1897,  pp.  302. 
