QUEBEC    NORTH    AND    WEST   OF   ST.    LAWRENCE    RIVER.  457 
Trenton).  The  thickness  of  the  upper  series,  exclusive  of  the  funda- 
mental gneiss,  is  placed  tentatively  as  50,000  to  G0,000  feet.  No  at- 
tempt is  made  to  estimate  the  thickness  of  the  underlying  gneiss  and 
syenite  series. 
Wilkins,20  in  1878,  describes  near  the  Grand  Trunk  station  of 
Shannonville,  about  three-fourths  of  a  mile  north  of  the  village,  a 
gray  and  green  slate  conglomerate  which  much  resembles  the  slate 
conglomerate  of  Lake  Huron  belonging  to  the  Huronian  system.  The 
base  of  this  rock  is  a  schistose  gray  orthoclase  with  green  hornblende 
and  epidote,  while  the  pebbles  are  of  Laurentian  gneiss,  white  and  red 
micaceous  and  syenitic  granite,  syenite,  felsite,  dolerite,  diorite,  epi- 
dote, chlorite,  and  quartz,  these  masses  being  generally  rounded,  par- 
ticularly 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  Gibsons  Mountain,  6  miles  southwest  of  Belleville,  occurs  Lauren- 
tian porphyritic  coarse-grained  granitoid  syenitic  gneiss. 
Selwyn,27  in  1879,  states  that  he  thinks,  without  having  personally 
examined  the  district,  that  it  has  been  conclusively  demonstrated  that 
the  Grenville  and  Hastings  groups,  consisting  of  limestones  and  cal- 
careous schists  holding  Eozoon,  with  associated  dioritic,  felsitic,  mi- 
caceous, slaty,  and  conglomeratic  rocks,  form  one  great  conformable 
series,  which  rests  unconformably  upon  a  massive  granitoid,  sye- 
nitic, or  red  gneiss  series,  and  is  unconformably  below  the  Potsdam  or 
Lower  Silurian  rocks.  The  same  may  be  said  of  the  Huronian  series 
of  Georgian  Bay,  which  at  Lake  Nipissing  includes  some  labradorite 
gneiss,  and  it  is  very  probable  that  a  connection  will  eventually  be  m 
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  anorthosites  are  believed  to  repre- 
sent the  volcanic  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, 
are  readily  understood.  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  stratigraphic  relations. 
Selwyn,28  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  garnet  if  erous,  pyroxenic  gneiss  banded 
like  Eozoon,  and  large  bands  of  crystalline  limestone.  These  rocks 
are  all  very  distinctly  stratified,  and  dip  generally  in  an  easterly 
direction  at  angles  varying  from  almost  horizontal  to  vertical. 
