vanhish.]  LAKE    HURON   TO    LAKE    TEMISCAMANG.  39 
rivers.  The  Huronian  is  found  to  be  in  two  main  troughs  and  the  thick- 
ness of  the  series  of  formations  amounts  to  16,700  feet.  This  thickness, 
greater  than  that  given  in  the  report  of  1857,  is  due  to  the  accidental 
existence  here  of  intercalated  greenstones. 
Bigsby,44  in  1802,  concludes  that  the  Huronian  is  greatly  older  than 
the  Cambrian  because:  (1)  Its  marked  similarity,  lithologically,  to  the 
fundamental  gneiss  formation.  (2)  The  conformity  of  these  two  sets  of 
beds.  (3)  The  great  interval  of  time  which  must  have  elapsed  between 
the  periods  of  laying  down  the  fundamental  formation  and  the  Silur- 
ian, if  we  are  to  judge  from  the  occasionally  vast  thickness  of  the  Cam- 
brian. Beyond  all  comparison,  the  Huronian  is  more  widespread  and 
extensive,  as  well  as  more  uniform  in  its  mineral  constitution,  than  the 
Cambrian  group.    It  is,  perhaps,  also  more  important  economically. 
Logan,12  in  1863,  gives  a  general  summary  of  the  information  as  to 
the  Huronian  series  north  of  lake  Huron.  This  area  is  mapped  in 
detail.  It  extends  along  the  entire  North  channel  of  lake  Huron,  with 
the  exception  of  a  short  distance  where  the  Laurentian  occupies  the 
shore.  The  full  section  on  the  north  shore  of  lake  Huron  is  as  fol- 
lows, from  the  bottom  upward:  (1)  gray  quartzite,  500  feet;  (2)  green 
chlorite  slate,  200  feet;  (3)  white  quartzite,  1,000  feet;  (4)  lower  slate 
conglomerate,  1,280  feet;  (5)  limestone,  300  feet;  (6)  upper  slate  con- 
glomerate, 3,000  feet;  (7)  red  quartzite,  2,300  feet;  (8)  red  jasper 
conglomerate,  2,150  feet;  (9)  white  quartzite,  2,970  feet;  (10)  yellow 
chert  and  limestone,  400  feet;  (11)  white  quartzite,  1,500  feet;  (12) 
yellowish  chert  and  impure  limestone,  200  feet;  (13)  white  quartzite, 
400  feet;  total  thickness,  18,000  feet.  Interstratiiied  with  certain  of 
these  layers,  and  particularly  Nos.  4,  6,  7,  8,  and  9  are  considerable 
masses  of  greenstone.  That  these  are  contemporaneous  overflows  in 
places  is  indicated  by  the  fact  that  they  are  amygdaloidal  and  are 
arranged  in  layers.  There  are,  however,  also  present  intrusive  masses 
of  greenstone  and  granite,  which  in  the  form  of  dikes  cut  the  stratified 
rocks  in  many  directions.  The  different  sets  of  dikes  are  of  at  least 
three  different  ages,  the  granite  being  intermediate  in  age  between  two 
greenstone  eruptions.  Many  of  the  pebbles  of  the  red  jasper  con- 
glomerate are  banded,  showing  their  derivation  from  a  more  ancient 
stratified  rock.  South  of  lake  Pakowagaming  is  a  considerable  area  of 
granite  which  breaks  through  and  disturbs  the  Laurentian  gneiss,  and 
from  which  emanates  a  complexity  of  dikes,  the  whole  being  supposed 
to  be  of  Huronian  age.  The  immediate  contact  of  the  gneiss  with 
the  overlying  rocks  has  not  been  observed.  The  gneiss  between  Mis- 
sissagui  and  St.  Marys  rivers  has  been  much  disturbed  by  intrusive 
granite  and  greenstone,  and  it  is  difficult  to  make  out  how  the  stratified 
portions  are  related  to  each  other.  Near  Les  Grandes  Sables,  a  gray 
quartzite,  supposed  to  be  the  lowest  Huronian,  abuts  against  one  mass 
of  gneiss,  and  runs  under  another  and  appears  to  be  much  broken  by 
and  entangled  among  the  intrusive  rock.    On  lake  Temiscamang  the 
