AREA    NORTH    AND    NORTHEAST    OF    LAKE    HURON.  407 
and  pebbles  of  syenite  and  jasper  are  found.  Eastward  of  Lake 
Temiscamang,  in  an  area  of  200,000  square  miles  imperfectly  exam- 
ined, no  similar  series  of  rocks  has  been  met  with.  Because  this 
clastic  series  of  rocks  occurs  in  typical  development  on  Lake  Huron 
it  has  been  decided  to  designate  it  by  the  term  Huronian. 
Murray,14  in  1859,  in  continuing  his  study  of  the  Huronian,  gives 
most  of  his  time  to  the  region  adjacent  to  the  Thessalon  and  Mis- 
sissagui  rivers.  The  Huronian  is  found  to  be  in  twTo  main  troughs, 
and  the  thickness  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,15  in  1862,  concludes  that  the  Huronian  is  greatly  older  than 
the  Cambrian,  because  of:  (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  forma- 
tion and  the  Silurian,  if  we  are  to  judge  from  the  occasionally  vast 
thickness  of  the  Cambrian.  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,10  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 
follows,  from  the  bottom  upward:  (1)  Gray  quartzite,  500  feet;  (2) 
green  chlorite  slate,  2,000  feet;  (3)  white  quartzite,  1,000  feet;  (4) 
lower  slate  conglomerate,  1,280  feet;  (5)  limestone,  300  feet;  (6) 
upper  slate  conglomerate,  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.  Interstratified  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  also  present,  howrever,  intru- 
sive 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  conglomerate  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 
