QUEBEC    NORTH    AXD    WEST    OF    ST.    LAWRENCE    RTVER.  459 
one  place  in  division  11  appears  a  band  of  highly  crystalline  lime- 
stone. 
At  many  places  the  Trenton  limestone  is  found  directly  in  contact 
with  the  Archean  rocks.  The  surface  of  the  Archean  rocks  on  which 
these  newer  beds  were  laid  down  had  a  rounded  undulatory  form, 
closely  resembling  the  present  exposed  surface.  The  gneisses  and  the 
limestone  present  fresh,  undecomposed  surfaces.  At  various  places 
betAveen  the  Trenton  limestone  and  the  Archean  is  a  thin  layer  of 
calcareous  sand  rock,  resting  in  the  hollows  of  the  Archean  surface, 
which  holds  Trenton  fossils.  In  one  place  in  the  limestone  is  found 
a  bowlder  of  gneiss  G  feet  long,  4  feet  wide,  and  4  feet  thick,  which 
is  supposed  to  have  been  dropped  by  floating  ice. 
Smyth,31  in  1893,  describes  pre-Cambrian  diabase  dikes  cutting 
the  granites  and  gneisses  of  the  Admiralty  group  of  the  Thousand 
Islands,  St.  Lawrence  River. 
Adams,32  in  1803,  describes  the  anorthosite  of  Canada,  and  gives 
its  relations  to  the  surrounding  rocks.  The  great  mass  of  the  Archean 
of  Canada  is  composed  of  an  orthoclase  gneiss,  which  is  in  many 
places  laminated,  but  is  in  large  part  little  laminated,  and  probably 
of  eruptive  origin.  Much  of  the  laminated  gneiss  is  probably  sedi- 
mentary. In  certain  regions  the  laminated  gneiss  is  interlaminated 
with  crystalline  limestones,  quartzite,  amphibolite,  etc.  This  series 
is  a  higher  part  of  the  Laurentian,  and  was  called  by  Logan  the 
Grenville  series;  while  the  lower  gneiss,  which  does  not  bear  any  of 
this  rock,  became  later  known  as  the  Ottawa  gneiss.  The  limestone, 
graphite,  etc.,  are  evidences  of  the  existence  of  life  during  the  depo- 
sition of  the  Grenville  series,  and  this  was  the  earliest  life  of  the 
planet. 
All  of  the  minerals  of  economic  importance  occur  in  the  Grenville 
series.  The  relations  of  the  Grenville  to  the  Ottawa  series  have  not 
been  certainly  determined,  but  it  is  probable  that  the  Grenville  series 
lies  discordantly  upon  the  old  gneiss,  the  upper  series  being  sediments 
originally  like  those  that  are  deposited  to-day. 
The  anorthosite  group,  or  Upper  Laurentian  of  Logan,  is  com- 
posed of  eruptive  rocks  belonging  to  the  gabbros.  It  is  characterized 
by  a  predominance  of  plagioclase,  which  frequently  is  the  only  min- 
eral of  the  rock.  The  rock  is  hard  and  originally  was  completely 
massive.  This  original  structure  has  been  modified  so  as  to  take  on 
an  extraordinary  cataclastic  structure,  which  has  also  given  the  rock  a 
schistose  character.  This  is  not  ordinary  dynamic  metamorphism, 
but  is  caused  by  a  movement  of  the  rock  mass  while  it  was  deeply 
buried  and  near  its  melting  point. 
The  anorthosite,  although  so  regarded  by  Logan,  is  not  a  distinct 
sedimentary  geological  formation,  but  cuts  through  both  the  gneiss 
and  the  limestone  of  the  Laurentian.     Its  intrusive  character  is  shown 
