242  rRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
Bobb,55  in  1876,  finds  that  a  massive  syenite  and  associated  crystal- 
line rocks  have  a  quite  widespread  distribution  in  cape  Breton.  At 
some  points  the  Carboniferous  rocks  are  brought  in  contact  with  the 
syenite,  but  generally  there  are  interposed  metamorphic  calcites,  argil- 
lites,  and  quartzites  associated  with  dolomites,  and  other  magnesian 
rocks,  which  are  in  a  vertical  or  highly  inclined  position,  and  evidently 
belong  to  a  pre- Carboniferous  altered  sedimentary  series.  The  junction 
of  the  pre-Carboniferous  limestones  with  the  syenite  is  approximately 
parallel  to  the  mountain  range,  but  is  locally  irregular,  and  in  some  in- 
stances the  limestones  seem  to  fill  depressions  in  the  syenite.  The 
Lower  Carboniferous  rocks  in  places  rest  directly  upon  the  syenite,  fill- 
ing the  hollows  in  it,  and  have  basal  conglomerates,  the  debris  of  which 
is  derived  from  the  overlying  syenite,  limestone,  and  quartzite. 
Fletcher,56  in  1877,  finds  in  cape  Breton,  below  the  Silurian  rocks, 
first,  a  set  of  syenitic,  gneissoid,  and  felsitic  rocks ;  and  second,  the 
George  river  limestone  series,  consisting  of  crystalline  limestones  and 
dolomites,  interstratified  with  felsite,  syenite,  diorite,  mica-schist,  quartz- 
ite, and  quartzose  conglomerate,  both  of  which  are  referred  to  the 
Laurentian,  although  the  latter  may  be  Huronian.  The  Lower  Silu- 
rian shales  lie  nearly  horizontally  upon  the  syenites  and  felsites  without 
any  appearance  of  alteration  and  without  being  intruded  by  the  felsites 
or  syenites.  The  crystalline  limestone  series  is  in  close  affinity  with 
the  feldspathic  group  of  rocks,  but  is  distinct,  as  is  shown  by  the  oc- 
currence of  pebbles  of  syenite  and  felsite  in  the  quartzose  conglomerate 
of  Murphy  brook. 
Fletcher,57  in  1878,  continues  his  study  of  the  pre-Cambrian  of 
cape  Breton  and  northern  Nova  Scotia.  The  George  river  limestone  is 
bounded  upon  both  sides  by  coarse  syenitic  and  granitic  rocks  and  is 
in  apparent  conformity  with  them. 
Dawson58  (Sir  William),  in  1878,  places  the  rocks  of  the  Bloisdale 
hills  iu  cape  Breton  as  older  than  the  Lower  Silurian,  and  it  is  not  im- 
possible that  rocks  of  the  same  age  may  occur  in  the  vicinity  of  the 
Cambrian  beds  at  Mire.  Also  the  chloritic  rocks  of  Yarmouth  may  con- 
jeeturally  be  placed  with  the  Huronian.  With  the  exception  of  the 
rocks  of  St.  Anns  mountain,  of  the  island  of  St.  Paul,  and  some  parts 
of  northern  cape  Breton,  no  rocks  are  found  which  are  regarded  as 
lithologically  equivalent  to  the  Laurentian  of  Canada. 
Fletcher,59  in  1879,  describes  the  pre-Primordial  rocks  as  occupying 
two  large  areas,  one  constituting  the  Mira  hills,  while  the  other  is  a  belt 
of  variable  width  along  the  shore  of  the  Atlantic.  There  are  two 
basins  of  metamorphic  rocks  running  parallel  to  the  felsite  series,  one 
of  which  abounds  in  Primordial  fossils  and  the  second  probably  of 
Devonian  age.  The  latter  contains  masses  of  granitoid  and  trappean 
rocks. 
Fletcher,60  in  1881,  in  continuing  his  studies  in  northern  Nova. 
Scotia,  again  divides  the  pre- Cambrian  rocks  into  two  groups.     In  the 
