464  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
marked  characteristics  of  this  district  is  the  great  development  of 
pyroxenic  and  hornblendic  rocks,  among  which  many  are,  without 
doubt,  of  eruptive  origin.  There  are  also  several  large  intrusive 
masses  of  granite  and  a  very  extensive  mass  of  nepheline  syenite. 
Otherwise  the  Hastings  and  Grenville  series  are  not  very  unlike 
petrographically. 
In  the  area  south  of  that  of  sheet  118,  in  Dalton  and  the  western 
part  of  Digby  townships,  is  found  reddish  orthoclase  gneiss  with 
dark  micaceous  and  hornblendic  bands,  which  is  cut  in  a  complicated 
way  by  coarse-grained  granite.  In  the  eastern  part  of  Digby 
Township  and  in  Lutterworth  and  Galway  townships  are  found 
crystalline  limestones  and  the  peculiar  rusty  weathering  gneisses 
always  associated  with  them.  In  the  limestone  districts  occur  various 
metalliferous  ores. 
Ells,36  in  1894,  states  that  the  mica  and  apatite  of  the  Laurentian 
of  Canada  are  confined  to  a  horizon  composed  of  a  series  of  gneisses 
which  constitute  the  upper  portion  of  the  Laurentian  siliceous  rocks 
and  which  underlie  the  limestone  proper.  This  horizon  grades  up- 
ward by  regular  passage  through  the  interstratification  of  calcareous 
layers  into  the  massive  crystalline  limestone  formation. 
Adams,37  in  1895,  describes  a  district  of  3,500  square  miles  of  pre- 
Cambrian  rocks  belonging  to  the  Grenville  series  immediately  east  of 
the  Original  Laurentian  area,  described  by  Logan  and  Ells,  and 
northwest  of  the  city  of  Montreal.  A  subordinate  part  of  the  area 
about  Trembling  Mountain  and  another  area  to  the  west  of  St.  Jerome 
are  referred  to  the  Fundamental  gneiss.  The  Grenville  series  occu- 
pies the  major  portion  of  the  district,  but  about  1,000  square  miles  are 
occupied  by  anorthosite,  which  occurs  in  one  large  area  known  as  the 
Morin  area  and  ten  smaller  masses.  The  Morin  anorthosite  incloses 
detached  masses  of  the  gneiss.  There  are  also  present  in  the  district 
one  mass  of  intrusive  syenite  covering  an  area  of  36  square  miles,  and 
a  much  larger  mass  of  granite  in  the  northeast  portion. 
The  Grenville  series  is  composed  of  rocks  in  well-defined  bands,  the 
whole  exhibiting  a  clear  foliation,  usually  parallel  to  the  banding. 
The  series  thus  has  a  decidedly  stratified  appearance,  similar  to  that 
presented  by  sedimentary  rocks.  The  gneiss,  which  on  the  west  side 
of  the  area  dips  at  an  angle  of  40°,  toward  the  east  becomes  nearly 
flat,  often  quite  so,  and  these  nearly  flat  gneisses  extend  to  the  north 
and  east  far  beyond  the  limits  of  the  map.  Throughout  this  area  of 
flat-lying  rocks  the  gneisses  with  their  interstratified  limestones  and 
quartzites  are  as  highly  crystalline  as  in  the  most  highly  contorted 
districts  and  have  evidently  undergone  an  extensive  stretching  or 
rolling  out,  resulting  in  the  tearing  apart  of  the  less  plastic  bands 
and  the  flowing  of  the  material  of  the  more  plastic  bands  into  the 
spaces  between  the  separated  fragments. 
