30  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA,  [bull. 86, 
Vennor,24  iu  1876,  gives  a  further  report  on  the  rear  portions  of  Froiir 
tenac  and  Lanark  counties.  Two  sections  are  given,  representing  the 
limestones  as  interstratified  with  the  quartzites  and  gneisses.  The  rocks 
are  classified  into  five  groups:  I,  Mica-schist  group ;  II,  Dolomite  and 
slate  group;  III,  Diorite  and  hornblende-schist  group;  IV,  Crystalline 
limestone  and  hornblende-rock  group;  V,  Gneiss  and  crystalline  lime- 
stone group.  A  sixth  group,  described  in  a  previous  report,  occupies 
the  front  portion  of  Lanark  county.  Each  of  the  five  groups  have 
many  subordinate  phases  of  rocks;  they  occupy  distinct  and  separate 
positions,  but  it  is  not  known  whether  they  represent  one  or  more  for- 
mations. 
Vennor,25  in  1877,  states  that  there  is  in  eastern  Ontario  and  the 
adjoining  portions  of  Quebec  an  Azoic  formation,  consisting  of  syenite 
and  gneiss(?),  without  crystalline  limestone,  in  which  there  is  but  little 
indication  of  stratification.  On  it  has  been  unconformably  deposited  a 
great  system  of  gneisses,  schists,  slates,  crystalline  limestones,  and 
dolomites,  in  the  higher  member  of  which  Eozoon  is  found.  The  lime- 
stone occurs  in  four  principal  belts.  Both  Logan's  Huronian  and  Upper 
Laurentian  are  considered  to  belong  to  the  second  division,  which  is  for 
the  present  called  the  Upper  Laurentian.  Interstratified  with  several 
of  the  bands  of  limestone  are  labradorite  rocks.  No  evidence  is  found 
for  making  these  a  distinct  system.  The  Huronian  and  Hastings  series 
are  simply  an  altered  condition  in  their  westward  extension  of  the 
lower  portion  of  the  upper  system. 
Vennor,26  in  1878,  reports  on  the  counties  of  Renfrew,  Pontiac,  and 
Ottawa.  Referring  to  the  work  of  previous  years,  it  is  said  that  the 
rocks  of  divisions  B  and  0  of  the  Hastings  series  are  really  the  western 
extensions  of  the  diorites,  hornblende-schists,  and  mica-slates  of  Lanark 
and  Renfrew  counties,  in  other  words,  of  groups  I,  II,  and  III;  and 
these  last  have  also  been  shown  to  be  a  low  portion  of  the  gneiss  and 
limestone  series,  that  is,  groups  IV,  V,  and  VI;  and  these  have  always 
been  looked  upon  as  typical  Laurentian.  The  conclusion  is  consequently 
reached  that  the  Hastings  series  is  not,  as  it  has  been  considered  to  be, 
the  most  recent,  but  rather  the  oldest  portion  of  this  great  system  of 
rocks  investigated.  It  is  also  clear  that  this  great  crystalline  gneiss 
and  limestone  series  rests  upon  a  still  older  gneiss  series,  in  which  no 
crystalline  limestones  have  yet  been  discovered.  This  series  is  the  one 
referred  to  as  division  A,  where  limestones  have  been  mentioned,  but 
incorrectly.  This  occupies  many  hundreds  of  square  miles  between  the 
St.  Lawrence  and  Ottawa  rivers,  and  is  the  rock  which  forms  the  back- 
bone of  eastern  Ontario  and  the  nucleus  around  which  have  been  de- 
posited all  succeeding  formations.  This,  then,  is  undoubtedly  Archean 
and  LoVer  Laurentian,  and  consequently  the  crystalline  limestones 
and  gneisses  constitute  a  series  which  would  come  in  beneath  Logan's 
Upper  Laurentian  or  Labradorite  series.  Whether  this  latter  exists 
as  a  distinct  formation  is  doubtful.    In  each  instance  in  which  the 
