van  iiisE.]  DISCUSSIONS    OF    PRINCIPLES.  477 
there  are  many  other  areas  in  which  there  are  between  the  Cambrian 
and  the  basal  complex  great  series  of  clastic  rocks,  although  the  evi- 
dence at  hand  in  favor  of  vast  age  for  the  basement  complex  is  less  than 
in  cases  before  cited.  Here  are  included  the  Front  range  of  Colorado, 
which  has  between  the  basal  complex  and  the  fossiliferous  rocks  on  its 
eastern  slope  the  clastic  series  of  Boulder,  Coal,  and  Thompson  creeks; 
and  the  Quartzite  mountains  of  Colorado,  where  between  the  basal  com- 
plex and  the  Carboniferous  is  a  great  series  of  quartzites.  There  is 
definite  structural  evidence  for  placing  these  and  other  areas  with  the 
group  first  considered.  In  a  third  class  of  areas  no  definite  evidence  in 
the  nature  of  intervening  series  shows  that  between  the  Cambrian  and 
the  basal  complex  has  intervened  an  era  or  even  a  period. 
Because  of  the  unique  lithological  character  of  this  fundamental  com- 
plex in  all  these  regions,  and  because  of  the  essential  likeness  in  struc- 
ture prevailing,  we  have  ground  for  grouping  these  rocks  together, 
whether  exactly  of  the  same  age  or  not.  Lithological  arguments  for 
correlation  may  be  well  distrusted ;  but  the  exceedingly  strange,  varied, 
and  complex  lithological  and  structural  characters  of  this  system,  the 
like  of  which  we  have  no  evidence  has  been  duplicated  anywhere  in  later 
times,  is  an  argument  of  great  weight.  In  the  complexity  of  its  parts 
and  the  implications  of  its  structure  it  gives  evidence  of  vast  antiquity. 
In  Algonkian,  Cambrian,  Silurian,  Devonian,  and  even  later  times, 
completely  crystalline  schists  have  been  produced  over  large  areas; 
but,  while  often  in  these  systems  no  evidence  now  remains  of  clastic 
characters,  they  rarely  if  ever  closely  resemble  this  fundamental  com- 
plex. A  clastic  series  was  in  the  beginning  of  its  history  of  necessity 
a  shale,  a  sandstone,  a  limestone,  a  chert,  or  some  other  form  of  sedi- 
ment and  often  containing  carbonaceous  material.  Cementation,  meta- 
somatism, dynamic  action  may  have  profoundly  changed  any  of  these 
deposits.  A  limestone  may  have  been  transformed  into  a  crystalline 
marble,  or  if  impure  into  a  hornblende  schist  containing  scarcely  a  rem- 
nant of  original  carbonate.  A  cherty  carbonate  of  iron  may  have  become 
an  actiHolite-niagnetite-schist.  Carbonaceous  shaly  material  may  have 
become  a  graphite- schist,  but  if  such  a  rock  is  represented  in  the  funda- 
mental complex  what  has  become  of  the  carbon?  A  sandstone  may 
have  become  a  granular  quartzite  or  a  foliated  micaceous  quartz- schist. 
But  that  a  great  quartzite  formation  like  those  of  the  Huronian  of  lake 
Superior  or  the  pre-Olenellus  of  the  Wasatch  can  have  become  wholly 
obliterated  by  any  process  short  of  fusion  is  almost  inconceivable.  As 
has  been  said,  none  of  these  rocks  are  found  in  this  fundamental 
complex  throughout  its  whole  vast  area.  In  its  positive  as  well  as 
its  negative  qualities  it  is  a  unit.  While  it  can  not  be  considered 
demonstrated  that  all  of  its  area  are  of  the  same  age,  it  may  then  be 
accepted  that  in  North  America  is  a  system  of  granites,  gneisses,  and 
crystalline  schists  which  are  the  oldest  rocks  of  North  America,  and 
which  have  representatives  in  many  areas  throughout  the  United  States, 
