28  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
Logan/5  in  1866,  further  describes  the  distribution  and  structure  of 
the  Ottawa  Laurentian  limestone.  There  are  here  three  great  conforma- 
ble bands,  which  are  termed  the  Grenville,  Green  lake,  and  Trembling 
lake  bands.     In  these  limestones  Eozoon  is  found. 
Logan,16  in  1867,  states  that  the  Hastings  series  is  arranged  in  the 
form  of  a  trough,  and  that  to  the  eastward,  and  probably  beneath  them, 
are  rocks  which  resemble  those  of  the  Grenville,  and  it  is  supposed 
that  the  Hastings  series  is  somewhat  higher  than  the  Grenville.  The 
Madoc  limestone  is  overlain  unconformably  at  several  places  by  the 
horizontal  Lower  Silurian  limestone.  In  Tudor  the  limestone  is  sud- 
denly interrupted  for  a  considerable  part  of  its  breadth  by  a  mass  of 
anorthosite  rock,  rising  150  feet  above  the  general  plain,  which  is  sup- 
posed to  belong  to  the  unconformable  Upper  Laurentian. 
Vennor,17  in  1867,  gives  the  ascending  section  of  Laurentian  rocks 
in  Hastings  county  as  follows:  Eed  feldspathic  gneiss,  5,000  feet  thick; 
dark  green  chloritic  slates,  200  feet;  crystalline  limestone,  2,200  feet; 
siliceous  and  micaceous  slates,  400  feet;  bluish  and  grayish  mica-slates, 
500  feet;  pinkish  dolomite,  100  feet;  micaceous  limestone  or  calc-schist, 
containing  Eozoon,  2,000  feet;  green  diorite  slates,  7,500  feet;  reddish 
granitic  gneiss,  2,100  feet;  total,  20,000  feet. 
Dawson18  (Sir  William),  in  1869,  stated  that  the  graphite  of  the  Lau- 
rentian is  scattered  through  great  thickness  of  limestones,  and  is  found 
also  in  veins.  In  one  bed  of  limestone  600  feet  thick  the  amount  of 
disseminated  graphite  must  amount  to  as  much  as  a  solid  bed  20  or  30. 
feet  thick.  The  graphite  is  believed  to  be  of  organic  origin  because, 
lirst,  it  contains  obscure  traces  of  organic  structure;  second,  its  arrange- 
ment and  microscopical  structure  corresponds  with  that  of  micaceous 
and  bituminous  matter  in  marine  formations  of  modern  date;  third,  if 
of  metamorphic  origin,  it  has  only  undergone  the  metamorphosis  which 
is  known  to  affect  organic  material  of  later  age;  fourth,  it  is  associated 
with  beds  of  limestone,  iron  ore,  and  metallic  sulphides,  presumably  of 
organic  origin. 
Vennor,19  in  1870,  in  a  report  on  Hastings  county,  describes  the  pre- 
Silurian  rocks.  The  rocks  are  divided  into  three  divisions,  A,  B,  and 
C.  A,  the  lower  division,  consists  of  syenite  rock,  granitic  gneiss,  2,000 
feet;  line-grained  gneiss,  sometimes  hornblendic  and  passing  into  mica- 
schist,  10,400  feet;  crystalline  limestone,  400  feet.  B,the  middle  divi- 
sion, is  of  hornblendic  and  pyroxenic  rocks,  including  diorite  and  dia- 
base, both  massive  and  schistose,  4,200  feet.  C,  the  upper  division, 
consists  of  crystalline  and  granular  limestone,  330  feet;  mica-slates  in- 
terstratified  with  dolomite,  sometimes  conglomeratic,  with  pebbles  of 
gneiss  or  quartzite  1  to  12  inches  in  diameter,  400  feet;  slate  inter  strat- 
ified with  gneiss,  500  feet;  gneissoid  micaceous  quartzites,  interstrati- 
fied  with  siliceous  limestone,  1,900  feet;  gray  micaceous  limestone,  1,000 
feet.  Total,  21,130  feet.  The  syenite  in  certain  localities  has  no  ap- 
parent marks  of  stratification.     Associated  with  the  above  rocks  are 
