QUEBEC    NORTH    AND    WEST    OF    ST.    LAWRENCE    RIVER,  479 
supposed  to  be  sedimentary  and  separated  from  the  "  Lower  Lauren - 
tian  "  by  an  unconformity.  Later  Canadian  geologists  ascertained 
the  igneous  and  intrusive  nature  of  the  anorthosite  and  have  re- 
stricted the  term  "  Lower  Laurentian  "  to  the  Ottawa  gneiss  and  the 
term  "Upper  Laurentian  "  to  the  Grenville  series.  In  1897  Adams, 
Barlow,  and  Ells  suggested  that  the  Grenville  series  has  a  position 
similar  to  that  of  the  Huronian  of  the  north  shore  of  Lake  Huron, 
without  implying  identity  in  age,  thus  practically  confining  the  term 
Laurentian  to  the  Ottawa  gneiss.  Adams  later  suggested  as  an  addi- 
tional possibility  that  the  Grenville  might  be  correlated  with  the  Kee- 
watin.  This  is  further  suggested  by  Miller  and  Knight's  work  in 
the  Hastings  district.  So  far  as  present  evidence  goes,  the  Grenville 
series  can  not  be  certainly  correlated  either  with  the  Huronian 
(Algonkian)  or  with  the  Keewatin  (Archean).  On  the  accom- 
panying map  (PI.  I)  the  Grenville  area  is  colored  as  unclassified 
pre-Cambrian. 
HASTINGS    DISTRICT. 
The  Hastings  district  includes  an  area  between  Ottawa  and  St. 
Lawrence  rivers  southwest  of  the  city  of  Ottawa,  extending  from 
Peterborough  and  Hastings  counties  on  the  southwest  to  Lanark  and 
Renfrew  counties  on  the  northeast. 
Occupying  large  portions  of  the  district  is  the  fundamental  gneiss, 
consisting  of  igneous  rocks  closely  allied  to  granites,  diorites,  and 
gabbros,  all  showing  more  or  less  distinct  foliation. 
With  these  are  associated  large  areas  of  sedimentary  rocks  similar 
to  those  of  the  original  Laurentian  district,  among  which  limestone 
is  the  most  abundant  rock.  As  in  that  district,  there  are  inter- 
stratified  mica  schists  and  mica  gneisses,  hornblende  schists  and  horn- 
blende gneisses,  quartz  schists,  and  marble;  mica  slates  are  also  found. 
There  is,  however,  the  great  difference  that  in  the  Hastings  area  the 
metamorphism  is  much  less  intense  and  in  certain  places  there  are 
conglomeratic  schists  and  gneisses.  These  may  be  seen  in  typical 
development  about  and  between  Madoc  and  Bridgewater.  These  con- 
glomerates contain  a  great  variety  of  pebbles,  including  granite, 
syenite,  amphibolite,  felsite,  gneiss,  marble,  quartz,  and  jaspilite. 
The  pebbles  of  the  conglomerate  vary  from  distinct,  well-rounded 
ones  to  those  which  are  flattened  in  a  remarkable  manner,  in  some 
cases  being  not  more  than  a  half  inch  broad  and  5  or  10  inches  long. 
Cut  in  certain  directions,  the  rock  containing  these  much  flattened 
pebbles  appears  to  be  a  jDerfect  crystalline  schist;  cut  in  another  di- 
rection, it  is  clearly  a  conglomerate  with  a  schistose  matrix.  The 
greater  diameters  of  the  flattened  fragments  invariably  accord  with 
the  direction  of  schistosity.  The  schist  conglomerates  grade  ;ii 
various  places  into  nonconglomeratic  crystalline  schists  or  gneisses. 
