vanhisr.1  EASTERN    ONTARIO    AND    WESTERN    QUEBEC.  25 
Logan,9  in  1858,  in  describing  the  Laurentian  of  Ottawa  thinks  it  prob- 
able that  it  can  be  divided  into  two  great  groups :  that  characterized 
by  the  presence  of  limestone  and  that  without,  and  the  latter  of  these 
groups  also  will  be  capable  of  subdivision.  Often  interstratified  with 
the  limestones  are  bands  of  quartzite  which  are  heaviest  near  the  junc- 
tion of  the  limestone  and  the  gneiss.  The  greatest  mass  of  quartzite 
is  beneath  the  limestone  and  is  400  feet  thick.  The  limestones  of 
the  Laurentian  are  influenced  in  their  strikes  and  dips  by  subsequent 
masses  of  igneous  rocks.  However,  to  these  rocks  as  a  whole,  as  well 
as  to  their  equivalent  throughout  Canada,  is  applied  the  term  Lauren- 
tian series,  from  the  Laurentide  range  of  mountains  from  lake  Huron  to 
Labrador,  which  are  comprised  of  this  rock. 
Logan,10  in  1859,  gives  an  elaborate  description  of  the  distribution  of 
the  limestones  along  the  Eouge  river.  There  are  found  to  be  two  belts 
which  are  regarded  as  interstratified  with  the  gneisses.  This  latter 
rock  is  sometimes  garnetiferous  and  occasionally  is  spoken  of  as  the 
quartzite.  The  total  thickness  of  rocks  exposed  on  the  Eouge  is  over 
22,000  feet,  of  which  over  5,000  is  limestone. 
Logan,11  in  1860,  finds  three  belts  of  limestone,  which  are  associated 
with  massive  orthoclase  gneiss,  mica-slate,  hornblende  rock,  and  quartz 
rock  together  15,000  feet  thick.  The  calcareous  bands  are  largely  asso- 
ciated with  labradorite,  and  beds  of  hornblende  rocks  and  quartz  rocks 
often  thickly  studded  with  pink  garnets.  One  of  the  beds  of  pure  white 
quartz  rock  is  a  thousand  feet  thick.  Certain  fossil-like  forms  have 
been  found  which  resemble  Stromatocerium.  The  strata  are  very  much 
folded. 
Logan,12  in  1863,  gives  a  general  account  of  the  pre-Potsdam  rocks, 
which  are  called  Azoic  and  are  divided  into  the  Huronian  series  and 
the  Laurentian  system.  In  the  Laurentian  system  are  included  anor- 
thosite,  orthoclase-gneiss,  granitoid  gneiss,  quartzite,  hornblende-schist, 
mica-schist,  pyroxene  and  garnet  rocks,  limestones  and  dolomites.  The 
anorthosites  are  composed  of  lime- soda  feldspar,  varying  in  compo- 
sition from  andesine  to  anorthite,  and  associated  with  pyroxene  or 
hypersthene.  The  orthoclase-gneiss  has  a  never  failing  constancy  in 
the  parallelism  of  its  mineral  constituents,  which,  however,  is  some- 
times obscure.  This  rock  is  usually  very  feldspathic  and  often  coarse 
grained.  With  the  feldspar  and  quartz  are  often  mica  and  hornblende. 
The  gneisses  appear  to  attain  several  thousand  feet  in  thickness,  but 
are  divided  at  unequal  intervals  by  hornblende  and  mica-schist  in 
which  the  stratification  is  more  distinct.  The  quartzites  are  in  consid- 
erable volume,  two  layers  of  which,  nearly  pure,  have  one  a  thickness 
of  400  and  the  other  a  thickness  of  600  feet.  The  masses  of  limestone 
are  generally  very  crystalline  and  coarse  grained,  but  sometimes  are 
saccharoidal.  The  bands  of  limestone  are  sometimes  of  great  thick- 
ness They  are  usually  not  pure,  but  contain  many  other  minerals, 
g  which  are  very  frequently  mica  and  graphite.  Among  the 
minerals  is  chondrodite.     The  iron   ore,    which  is  mostly  mag- 
