454.  PRE-CAMBRIAN   GEOLOGY   OF    NORTH    AMERICA. 
B,  and  C.  A,  the  lower  division,  consists  of  syenite  rock,  granitic 
gneiss,  2,000  feet;  fine-grained  gneiss,  sometimes  hornblendic  and 
passing  into  mica  schist,  10,400  feet;  crystalline  limestone,  400  feet. 
B,  the  middle  division,  is  of  hornblendic  and  pyroxenic  rocks,  in- 
cluding diorite  and  diabase,  both  massive  and  schistose,  4,200  feet. 
C,  the  upper  division,  consists  of  crystalline  and  granular  limestone, 
330  feet;  mica  slates  interstratified  with  dolomite,  sometimes  con- 
glomeratic, with  pebbles  of  gneiss  or  quartzite  1  to  12  inches  in  diam- 
eter, 400  feet;  slate  interstratified  with  gneiss,  500  feet;  gneissoid 
micaceous  quartzites,  interstratified  with  siliceous  limestone,  1,900 
feet;  gray  micaceous  limestone,  1,000  feet.  Total,  21,130  feet.  The 
syenite  in  certain  localities  has  no  apparent  marks  of  stratification. 
Associated  with  the  above  rocks  are  deposits  of  iron  ore.  Eozoon 
xanadense  occurs  in  the  topmost  member  of  the  upper  division  (C). 
Division  B  rests  immediately  upon  A,  but  whether  conformably  or 
not  is  not  determined,  as  the  basal  members  of  B  are  massive  diorites 
and  greenstones. 
Vennor,19  in  1872,  applies  to  the  lowest  division  of  the  Hastings 
series  (A)  the  term  Laurentian,  and  the  middle  division  (B)  is 
placed  as  probable  Huronian.  The  rocks  of  the  upper  group  are 
found  to  lie  unconformably  upon  the  gneisses  and  crystalline  lime- 
stones of  the  lower  group,  and  it  is  probable  that  the  middle  group 
is  unconformably  below  the  upper  and  unconformably  above  the 
lower  group. 
Vennor,20  in  1872,  reports  on  Leeds,  Frontenac,  and  Lanark  coun- 
ties, Ontario.  The  granite  of  the  gold-bearing  rocks  is  believed  to 
represent  eruptions  which  took  place  probably  toward  the  close  of 
the  Laurentian  period,  or  at  some  time  prior  to  the  deposition  of  the 
rocks  of  divisions  B  and  C,  for,  whenever  these  higher  rocks  are 
wanting,  the  Laurentian  gneisses,  quartzite,  and  limestone  are  cut  by 
a  network  of  veins. 
Vennor,21  in  1873,  gives  an  additional  report  on  the  counties  of 
Frontenac,  Leeds,  and  Lanark.  The  area  is  divided  into  western, 
middle,  and  eastern  sections.  In  the  western  section  the  main  mass 
of  rocks  is  of  granite,  syenite,  and  coarse-grained  and  fine-grained 
gneisses.  The  red  granites  sometimes  appear  to  be  of  later  date  than 
the  white  mica  granites  and  even  of  the  diorites  of  division  B.  Lime- 
stone was  not  observed.  In  a  trough  between  two  granite  and  gneiss 
areas  are  found  diorite  slates,  micaceous  and  chloritic  schists,  pyrox- 
enic rocks,  conglomerates,  dolomites,  and  sandy  crystalline  limestones. 
In  one  conglomerate  the  pebbles  of  quartz  in  a  matrix  of  sand  and 
mica  are  flattened  out  along  the  plane  of  bedding,  so  that  those  which 
in  cross  measurement  are  not  more  than  half  an  inch  broad  have  a 
length  of  5  to  10  inches.  In  places  in  the  conglomerate,  instead  of 
pebbles,  are  layers  of  vitreous  quartz  or  quartzite  and  mica  schist.  The 
