686  PRE-CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA. 
naturally  referable  to  local  fractures  and  displacements,  and  this 
unconformableness  is  local  and  not  the  rule.  There  is  no  reason 
for  believing  that  the  metamorphosed  beds  include  formations  of 
any  more  recent  date  than  the  Ocoee  conglomerates  and  slates,  and 
a  portion  of  them  are  certainly  referable  to  this  group.  The  re- 
mainder, although  conformable,  may  be,  and  most  likely  are,  older. 
The  transitions  from  the  slates  and  conglomerates  to  the  gneiss  and 
mica  schists  are  well  seen  at  Ducktown  and  at  the  Ocoee.  There  is 
no  sufficient  reason  for  referring  any  of  these  rocks  to  the  Huronian 
or  the  Laurentian. 
Bradley,83  in  1875,  describes  sections  in  East  Tennessee  from 
Athens  to  Murphy  and  from  Knoxville  to  Murphy.  The  rocks  in- 
clude semimetamorphosed  slates,  like  those  of  Ocoee,  quartzites, 
crystalline  limestones,  and  gneisses,  all  being  regarded  as  probably 
of  Silurian  age,  with  the  possible  exception  of  the  massive  granite 
at  Marietta,  Cobb  County,  Ga.  The  Silurian  rocks  thus  include  the 
Taconic  and  pyroclastic  rocks  of  Emmons. 
Keith,84  in  1895,  maps  and  describes  the  geology  of  the  Knox- 
ville quadrangle,  in  Tennessee  and  North  Carolina,  and  of  the  Lou- 
don quadrangle,  in  Tennessee.  Ocoee  rocks  form  the  mountain  areas. 
From  the  base  upward  the  series  comprises  the  Wilhite  slate,  Citico 
conglomerate,  Pigeon  slate,  Cades  conglomerate,  Thunderhead  con- 
glomerate, Hazel  slate,  and  Clingman  conglomerate. 
The  Wilhite  slate  is  bluish-gray  or  black  argillaceous  slate.  In  its 
upper  portion  it  becomes  calcareous,  and  contains  numerous  beds  of 
limestone  and  limestone  conglomerate.  The  thickness  is  ordinarily 
from  300  to  400  feet.  The  Citico  conglomerate  is  entirely  siliceous, 
and  varies  from  fine  white  sandstone  to  coarse  quartz  conglomerate, 
with  a  few  thin  beds  of  sandy  shale.  The  Pigeon  slate  is  mainly  an 
argillaceous  slate  of  great  uniformity,  occasionally  banded  by  thin 
seams  of  coarser  siliceous  material.  The  thickness  varies  from  1,300 
to  1,700  feet. 
The  Cades  conglomerate,  Thunderhead  conglomerate,  Hazel  slate, 
and  Clingman  conglomerate  are  not  described  for  the  Loudon 
quadrangle. 
In  the  Knoxville  quadrangle  the  Cades  conglomerate  consists  of 
thick  beds  of  slate,  sandstone,  graywacke,  and  conglomerate.  The 
apparent  thickness  is  2,400  feet,  but  this  may  be  an  overestimate, 
because  the  formation  may  be  repeated  by  folding.  The  Thunderhead 
conglomerate  consists  of  a  series  of  conglomerates,  graywackes,  and 
sandstones,  with  many  small  beds  of  slate.  The  thickness  is  believed 
to  be  about  3,000  feet.  The  Hazel  slate  is  chiefly  a  black  slate,  but  it 
contains  many  thin  beds  of  sandstone  and  conglomerate  in  small 
quantity.  The  exact  thickness  can  not  be  ascertained,  but  it  is  be- 
lieved to  be  about  700  feet.    The  Clingman  conglomerate  is  the  same 
