504  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [Btjk.M 
MISSOURI. 
The  Algonkian  elastics  of  Missouri  are  a  group  of  isles  surrounded 
by  Paleozoies.  Tliey  consist  of  limestones,  slates,  iron  ores,  and  con- 
glomerates, the  most  of  the  debris  of  which  is  from  porpliyries  and  are 
interbedded  with  surface  quartz-porphyry  flows,  which  make  up  the 
greater  part  of  the  volume  of  the  series.  There  are  here  also  granites, 
which  are  probably  of  the  same  age.  If  this  is  the  case  no  rocks  older 
than  the  Algonkian  are  here  known.  The  series  shows  conclusive  evi- 
dence of  vast  denudation  before  the  horizontal  Cambrian  was  deposited 
upon  it.  The  lithological  character  of  the  series  is  intermediate  be- 
tween the  Upper  Huronian  and  Keweenawan  of  the  lake  Superior 
region,  and  it  may  stand  as  the  equivalent  of  one  or  the  other  of  these, 
or  in  an  intermediate  position. 
TEXAS. 
In  Texas  the  Algonkian  is  represented  by  the  Llano  series  of  Wal- 
cott  or  the  Texian  series  of  Comstock  and  by  the  Fernandian  of  Corn- 
stock.  The  first  series  consists  of  gently  folded  shales,  sandstones, 
limestones,  and  schists  with  ferruginous  beds,  and  is  cut  by  both  basic 
and  acid  eruptives.  It  is  for  the  most  part  very  little  metamorphosed, 
and  is  said  to  repose  unconformably  upon  the  Fernandian.  The  Fer- 
nandian series  consists  of  quartzites,  ferruginous  rocks,  carbonaceous 
schists,  chloritic  slates  and  shales,  calcareous  rocks,  and  other  acidic 
and  basic  schists.  It  is  now  a  rather  crystalline  series,  but  it  is  clearly, 
in  part  at  least,  of  clastic  origin.  The  series  is  cut  by  numerous  erup- 
tives, both  basic  and  acidic,  of  which  granite  is  the  most  prominent.  As 
to  the  relations  of  the  clastic  series  to  the  Burnetian  (Archean),  they 
are  believed  by  Comstock  to  be  unconformably  above  it.  They  are 
separated  by  a  great  unconformity  from  the  Cambrian  sandstone. 
Comstock  correlates  the  Texian  with  the  entire  Grand  canyon  clastic 
section,  which,  if  true,  and  the  above  supposed  relations  correct,  make 
the  Fernandian  rather  low  Algonkian. 
MEDICINE  BOW  RANGE. 
In  the  Medicine  Bow  mountains,  the  clastic  series  of  Medicine  and  Mill 
peaks,  consisting  of  slates,  cherts,  siliceous  limestones,  quartzites,  and 
conglomerates,  all  of  considerable  thickness,  appear  to  be  conformable 
with  the  more  crystalline  granite-gneiss  complex.  The  only  evidence 
that  there  is  a  break  between  the  two  is  the  presence  of  granite  and 
gneiss  fragments  in  the  lower  parts  of  the  clastic  series.  In  degree  of 
crystallization  and  lithological  character  this  Algonkian  series  is  like 
the  Lower  Huronian  of  the  lake  Superior  country. 
SOUTHWESTERN   MONTANA. 
Tn  southwestern  Montana  the  Algonkian  is  probably  represented  by 
two  series.     The  upper  series  consists  of  12,000  or  15,000  feet  of  unal- 
