32  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull.  SB. 
rock  is  a  schistose  gray  orthoclase  with  green  hornblende  and  cpidote, 
while  the  pebbles  are  of  Laurentian  gneiss^  white  and  red  micaceous 
and  syenitic  granite,  syenite,  felsite,  dolerite,  diorite,  epidote,  chlorite, 
and  quartz,  these  masses  being  generally  rounded,  particularly  the 
gneissic  pebbles,  and  very  rarely  angular,  while  in  size  some  exceed  a 
foot  in  diameter,  and  others  are  not  over  2  or  3  inches.  At  Gibson's 
mountain,  6  miles  southwest  of  Belleville,  occurs  Laurentian  porphyritic 
coarse  grained  granitoid  syenitic  gneiss. 
Selwyn,29  in  1879,  states  that  it  has  been  conclusively  demonstrated 
that  the  Grenville  and  Hastings  groups,  consisting  of  limestones  and 
calcareous  scbists  holding  Eozoon,  with  associated  dieritic,  felsitic,  mi- 
caceous, slaty,  and  conglomeratic  rocks,  form  one  great  conformable 
series,  which  rests  quite  unconformably  upon  a  massive  granitoid,  syen- 
itic, or  red  gneiss  series,  and  are  unconformably  below  the  Potsdam  or 
Lower  Silurian  rocks.  The  same  may  be  said  of  the  Huronian  series 
of  Georgian  bay,  which  at  lake  Nipissing  include  some  labradorite 
gneiss,  and  it  is  very  probable  that  a  connection  will  eventually  be 
traced  out  between  these  supposed  greatly  different  formations  like  that 
now  proved  to  exist  between  the  Hastings  and  Grenville  series.  The 
Norian  series  is  thought  to  be  a  part  and  parcel  of  the  great  crystalline 
limestone  series.  These  anorthosifces  are  thought  to  represent  the  vol- 
canic and  intrusive  rocks  of  the  Laurentian  period,  and  if  so,  their 
massive  and  irregular,  and  sometimes  bedded  appearance,  and  the  fact 
that  they  interrupt  and  cut  off  some  of  the  limestones,  is  readily  under- 
stood. Chemical  and  microscopical  investigations  both  seem  to  point 
to  this  as  the  true  explanation  of  their  origin.  That  they  are  really 
eruptive  rocks  is  held  by  nearly  all  geologists  who  have  carefully 
studied  their  stratigraphical  relations. 
Selwyn,30  in  1884,  finds  from  Pembroke  to  Wahnahpitae  river  on 
the  Canadian  Pacific  railway,  nothing  but  Laurentian,  which  consists 
of  red,  gray,  and  white  orthoclase  gneiss,  black  hornblende-schists  and 
mica-schists,  often  garnetiferous,  pyroxenic  gneiss  banded  like  Eozoon, 
and  large  bauds  of  crystalline  limestone.  These  rocks  are  all  very  dis- 
tinctly stratified,  and  dip  generally  in  an  easterly  direction  at  angles 
varying  from  almost  horizontal  to  vertical. 
SUMMARY   OF    RESULTS. 
It  is  apparent  that  the  great  area,  roughly  bounded  by  Georgian  bay, 
the  Ottawa  and  St.  Lawrence  rivers,  to  which  the  term  Laurentian  is 
applied,  is,  as  a  whole,  a  very  crystalline  one.  This  is  so  far  true  that  no 
attempt  has  been  made  over  the  greater  part  of  the  area  to  stratigraph- 
ically  subdivide  the  rocks.  The  exceptions  to  this  are  a  small  area  in 
Argenteuil  and  adjacent  counties,  and  a  strip  of  country  running  from 
Ottawa  to  Madoc.  Even  in  the  districts  in  which  the  detailed  maps 
are  given  there  is  no  estimate  of  the  thickness  of  the  layers  of  the  more 
massive  parts  of  the  series. 
