44  PRE-CAMBRTAN    ROCKS    OF    NORTH    AMERICA.  |bull.  86. 
varieties  of  graywacke  may  be  seen  passing  into  thoroughly  crystalline 
quartz-syenite.  The  rocks  in  greatest  quantity,  and  those  which  con- 
stitute the  lowest  member  of  the  Huronian  series  between  lakes  Huron 
and  Wahnapitae,  are  quartzose  graywackes  and  quartzites,  with  occa- 
sionally a  little  felsite.  In  this  member  of  the  series  crystalline  diorites 
occur  as  intruded  masses,  varying  from  a  half  a  mile  to  ten  miles  in 
length.  Also  are  associated  obscurely  stratified  varieties  of  quartz- 
diorite  and  of  dioritic  and  hornblendic  schists,  and  also  compact  brown- 
weathering  dolomite.  The  next  member  of  the  series  in  ascending  order 
is  a  black  volcanic  glass  breccia  consisting  of  angular  fragments  crowded 
together.  The  highest  rocks  of  the  series,  or  those  which  occupy  the 
center  of  the  trough,  are  evenly  bedded  argillaceous  sandstones  or  gray- 
wackes, inter  stratified  with  slaty  belts  and  overlain  at  the  summit  by 
black  slates.  The  stratified  Huronian  rocks,  as  well  as  the  gneiss  and 
quartz- syenite,  are  traversed  by  dikes  of  coarsely  crystalline  diabase, 
which  are  often  large  and  can  be  traced  for  considerable  distances. 
Winchell  (N.  H.),55in  1891,  gives  further  observations  upon  the  Hu- 
ronian. Northwest  of  Sudbury  and  eastward  from  Algoma  there  are 
two  formations.  In  both,  the  slate  and  slate  conglomerate  constitute 
the  upper  formation.  In  the  Sudbury  region  the  underlying  rocks  are 
largely  felsitic,  but  are  also  occasionally  micaceous  and  hornblendic. 
In  the  section  eastward  from  Algoma  the  underlying  formation  seems 
to  be  the  Mississagui  quartzite,  with  interbedded  green  fissile  schist, 
with  mica-schist  varying  into  hornblende- schist.  Logan's  Mississagui 
quartzite  is  supposed  not  to  be  Logan's  lowest  gray  quartzite,  but 
is  probably  a  constituent  part  of  the  Keewatin.  It  is  concluded  that 
the  observations  confirm,  or  at  least  do  not  contravene,  the  conclusion 
that  the  Huronian  system  of  the  Canadian  reports  embraces^ two  or 
three  formations,  one  of  these  the  true  Huronian,  first  described  and 
mapped  by  Murray ;  another,  the  Keewatin  of  Lawson;  and  another, 
the  series  of  crystalline  schists  styled  the  Vermilion  series. 
Pumpelly  and  Van  Hise,56  in  1892,  describe  the  relations  of  the  Hu- 
ronian and  Laurentian  and  also  give  evidence  for  the  divisibility  of 
the  Huronian  into  two  series  as  advocated  by  Winchell. 
In  reference  to  the  latter  point,  at  a  limestone  quarry  about  2  miles 
northeast  of  Garden  river,  the  upper  slate  conglomerate  was  found  in 
actual  contact  with  the  limestone  member.  This  conglomerate  has  a 
rough  appearance  of  stratification  and  bears  numerous  fragments  of 
limestone,  many  of  them  more  than  a  foot  in  length  and  all  in  precisely 
the  condition  in  which  is  now  the  original  limestone.  In  this  conglom- 
erate are  also  numerous  fragments  of  schist  and  granite.  The  line  of 
contact  could  be  traced  only  a  short  distance,  and  it  appears  to  follow 
somewhat  closely  the  lamination  of  the  limestone.  These  relations 
clearly  indicate  that  after  the  limestone  was  deposited,  before  the  be- 
ginning of  the  time  of  the  upper  slate  conglomerate,  there  was  a  con- 
siderable interval  of  erosion.    The  observations  thus  tend  to  confirm 
