510  PKE-CAMBMAN    GEOLOGY    OF    NORTH    AMERICA. 
2.  Slate  division  : 
(a)  Greenish-gray  slates,  becoming  blnish  or  light  gray,  and  passing  into 
purple  slates,  or  becoming  clouded  or  zoned  with  shades  of  green, 
purple,  blue,  buff,  or  pale  yellow,  often  producing  a  conspicuous  rib- 
boning of  the  beds.  The  occurrence  of  light  yellowish-green  seams  is 
a  characteristic  feature  of  the  purple  slates. 
(&)  Bluish-gray  and  blue  slates,  with  lighter  gray  seams  or  bands,  and  in- 
cluding in  places  an  upper  zone  of  purple  slates. 
(c)  Black,  with  some  blue  or  gray,  slates,  often  highly  pyritiferous.  In 
metamorphic  regions  the  green  slates  are  represented  by  chloritic 
and  hornblendic  schists  (or  locally  by  conglomerates  with  a  mica- 
ceous or  hornblendic  base)  :  the  slaty  beds,  by  micaceous,  garnetif- 
erous,  and  andalusitic  schists. 
Above  the  Cambrian  rocks  are  those  belonging  to  the  Devonian 
system.  There  are  several  important  areas  of  granite — those  of 
South  Mountains,  Blue  Mountains,  Tusket  Wedge,  the  Barrington 
area,  Kelvin  area,  and  Port  Mouton  area.  These  are  intrusive  within 
the  Cambrian,  and  in  places  they  clearly  penetrate  and  alter  the  fos- 
siliferous  Lower  Oriskany  and  Silurian  rocks. 
Bailey,04  in  1898,  reports  on  the  geology  of  southwestern  Nova 
Scotia.  Cambrian  rocks  devoid  of  fossils  occupy  a  large  part  of  the 
area.    The  succession  is  as  follows,  in  ascending  order: 
1.  Quartzite  division  : 
(a)  Heavily  bedded  bluish  quartzites,  alternating  with  much  thinner  beds 
of  argillite. 
(&)  Greenish-gray  sandstones  or  quartzites,  somewhat  chloritic  and  less 
massive  than  in  (a),  and  alternating  with  slates  which  are  arena- 
ceous below  but  become  progressively  more  argillaceous  above. 
2.  Banded  argillite  division: 
(a)    Greenish-gray    slates,    becoming    bluish    or    light    gray,    and    passing 
upward  into — 
(&)    Purple  slates,  marked  in  the  lower  beds  by  pale,  yellowish-green  seams, 
with  faint  bedding  lines,  which  are  wanting  in  the  higher  beds, 
(c)   Bluish-gray   and   gray   slates,   often   with   cloudings   of  green,    purple, 
lilac,  buff,  or  yellow,  in  places  exhibiting  a  conspicuous  banding  or 
ribboning  of  the  beds. 
3.  Black  slate  division  : 
Black  slates,  with  some  blue  or  gray,  often  studded  with  cubes  of  pyrites, 
and  very  rusty  weathering. 
Faribault,05  in  1899-1905,  estimates  the  area  of  gold-bearing  series 
at  8,500  square  miles,  including  3,500  square  miles  of  intrusive 
granite,  leaving  5,000  square  miles  of  gold  measures  proper.  Intru- 
sion of  granite  occurred  at  the  clohc  of  the  Silurian,  probably  Oris- 
kany, and  was  accompanied  and  followed  by  disturbances,  faults,  and 
much  local  metamorphism  of  the  stratified  rocks.  It  occurred  after 
the  folding  of  the  sediments  and  the  deposition  of  the  auriferous 
quartz  veins.  No  well-defined  fossils  have  so  far  been  found,  but 
the  sediments  are  generally  ascribed  to  the  Lower  Cambrian  on  ac- 
count of  their  analogy  with  the  Harlech  grit  and  Lin  (/via  flag  series 
of  North  Wales,  the  auriferous  Cambrian  of  Quebec,  and  Murray's 
