516  PRE-CAMBRIAN    GEOLOGY   OF   NORTH   AMERICA. 
In  the  Laurentian  are  placed  the  gneisses  of  Conception  Bay,  the 
masses  of  granite,  syenite,  and  porphyries  of  St.  Johns  Peninsula  de- 
scribed by  Jukes,  and  the  granites  of  Placentia  Bay  and  Sound 
Island.  These  rocks  are  like  those  referred  to  the  Laurentian  in  the 
great  northern  peninsula.  The  intermediate  system  consists  of 
diorites,  quartzites,  slate  conglomerates,  slate,  and  sandstone,  the 
whole  series  in  Conception  Bay  being  more  than  11,000  feet  thick. 
This  series  resembles  lithologically  the  Huronian  system  of  Canada 
in  a  high  degree,  although  it  may  be  admitted  that  lithological  rela- 
tions are  of  secondary  importance  in  correlating  rocks  which  are  re- 
mote from  each  other.  In  one  member  of  the  group  is  a  fossil,  desig- 
nated Aspidella,  of  a  low  order  of  existence,  which  leads  to  the  con- 
clusion that  the  system  is  probably  Cambrian.  This  series  of  rocks 
occupies  by  far  the  greater  part  of  the  peninsula  of  Avalon.  The 
lower  rocks  in  all  cases  pitch  at  a  very  high  angle  to  the  horizon,  the 
prevailing  inclination  being  eastward,  while  the  upper  formation, 
except  where  disturbed  by  eruptives,  is  either  in  a  perfectly  horizontal 
attitude  or  only  slightly  inclined.  .The  lower  series  is  also  marked  for 
its  general  absence  of  lime,  while  the  upper  formation  is  nearly  all 
more  or  less  calcareous.  Further,  the  Potsdam  rocks  were  found  to 
overlie  unconformably  the  lower  slates  at  Manuels  Brook  and  at 
Brigus  South  Head.  The  Nova  Scotia  gold-bearing  rocks  are  litho- 
logically like  the  system  referred  to  the  Huronian  in  Newfoundland, 
although  they  have  been  referred  to  the  Lower  Silurian. 
Murray,75  in  1870,  finds  the  rocks  of  Bonavista  Bay  to  consist 
largely  of  slates,  slate  conglomerates,  quartzites,  and  diorites,  inter- 
sected by  intrusive  granite  or  syenite,  trap,  and  quartz  veins.  This 
series  has  such  a  close  lithological  resemblance  to  the  intermediate 
system  of  Avalon  that  there  is  no  doubt  of  their  identity.  These 
rocks  also  occur  between  the  gneiss  and  the  Paleozoic  formations  of 
Trinity  Bay. 
Howley,76  in  1870,  describes  sundry  parts  of  the  coast.  The  rocks 
of  Cape  Kay  and  the  extreme  head  of  Conception  Bay  are  of  a 
gneissoid  character.  Granite,  syenite,  and  trap  are  interbanded  with 
quartzite.  On  Great  Miquelon  Island  is  found  gneiss,  supposed  to  be 
of  Laurentian  age.  Greenstones  and  granite  break  at  various  places 
through  the  stratified  rocks. 
Murray,77  in  1873,  gives  a  further  account  of  the  Avalon  Peninsula. 
The  line  of  contact  between  the  Huronian  and  more  recent  rocks  in 
Trinity  Bay  is  obscure  and  difficult  to  detect,  and  here  Aspidella  is 
very  useful  in  deciding  to  which  series  the  rocks  belong.  The  rocks 
on  the  west  coast  of  Trinity  Bay  are  correlated  with  the  Huronian 
on  lithological  evidence.  The  rocks  here  are  in  some  respects  differ- 
ent from  those  on  St.  Johns  Peninsula,  but  this  difference  seems  to 
be  due  to  the  intense  volcanic  activity  which  has  affected  the  western 
