QUEBEC    NORTH   AND   WEST   OF   ST.   LAWRENCE   RIVER.  475 
These  granite  intrusions  form  part  of  the  typical  Laurentian  gneiss 
of  the  northern  protaxis,  which  stretches  far  away  in  an  unbroken 
mass  toward  the  pole.  The  limestone,  on  the  other  hand,  has  in 
certain  places  been  found  in  a  comparatively  unaltered  condition, 
in  which  case  it  is  fine  in  grain  and  dark  grayish  blue  in  color. 
Since  the  more  metamorphosed  varieties  of  the  limestone  series  are 
in  all  respects  similar  to  the  Grenville  series  of  the  Original  Lauren- 
tian district,  it  is  believed  that  the  Hastings  limestone  series  is  the 
equivalent  of  the  Grenville  series. 
In  addition  to  the  limestone  and  amphibolite,  etc.,  and  the  invad- 
ing gneissic  granite,  an  extensive  development  of  nepheline  syenite  is 
found  in  this  region.  This  rock  lies  almost  invariably  along  the 
contact  of  the  granite  batholiths  with  the  limestone,  although  it  does 
not  occur  by  any  means  continuously  along  this  contact.  The  nephe- 
line syenites  are  seen  to  eat  into  the  limestone  in  many  places  and  to 
hold  inclusions  of  the  limestone.  Its  manner  of  occurrence  indicates 
that  this  nepheline  syenite  forms  a  peripheral  phase  of  the  granite 
intrusions.  Like  the  granites,  the  nepheline  syenite  in  places  is  found 
to  have  a  very  coarse-grained  pegmatitic  development.  In  these 
nepheline  syenite-pegmatites  at  one  locality,  in  the  township  of 
Glamorgan,  individuals  of  nepheline  more  than  a  yard  in  diameter 
were  found.  At  some  points  the  magma  is  extremely  rich  in  alumina, 
so  much  so  that  its  crystallization  has  led  to  a  development  of  a 
corundum  syenite.  Elsewhere  the  syenite  contains  lenticular  veins  or 
masses  of  sodalite,  of  large  dimensions.  The  corundum  syenite  is 
now  being  worked  extensively  at  Craigmont  for  corundum,  while  a 
short  distance  east  of  the  town  of  Bancroft  the  sodalite  syenite  is 
being  worked  for  the  production  of  sodalite  as  an  ornamental  stone. 
Adams,  Barlow,  Coleman,  Cushing,  Kemp,  and  Van  Hise,  in 
1907,  report  on  the  correlation  of  the  pre-Cambrian  rocks  of  the 
Adirondack  Mountains,  the  "  Original  Laurentian  area  "  of  Canada 
and  eastern  Ontario.  See  summary  in  Chapter  X,  section  1,  The 
Adirondack  Mountains. 
Miller  and  Knight,50  in  1907,  find  the  Keewatin  series  of  the  Lake 
Superior  region  represented  in  southeastern  Ontario  by  ancient  rocks 
of  like  character.  The  Grenville  limestones  have  been  deposited  on 
the  surface  of  the  Keewatin.  Overlying  the  Grenville  limestone  un- 
conformably  are  the  Hastings  series  of  conglomerates,  limestones,  and 
other  sediments  provisionally  classed  as  Huronian.  The  Grenville 
limestones  are  regarded  as  having  the  same  relations  to  the  Keewatin 
greenstones  as  do  the  iron  formations  of  the  Lake  Superior  Keewatin. 
Adams,57  in  1908,  discusses  the  general  features  of  the  Grenville 
series  of  eastern  North  America  and  shows  that  it  covers  an  area  of 
at  least  83,000  square  miles,  making  it  the  greatest  development  of 
limestone  known  in  the  pre-Cambrian  of  North  America  and  one  of 
