van  His*.!  DISCUSSIONS    OF    PRINCIPLES.  509 
SUBDIVISIONS   OF   ALGONKIAN. 
The  foregoing  review  of  the  occurrences  of  pre-Cambrian  clastic 
rocks  makes  apparent  the  propriety  of  introducing  the  term  Agnoto- 
zoic  or  Proterozoic  to  cover  the  series  between  the  Paleozoic  and 
Archean.  The  desirability  of  dividing  the  group  into  several  systems 
is  also  apparent,  but  it  is  equally  apparent  that  our  limitations  of 
knowledge  at  the  present  time  make  it  impossible  to  do  this  for  the 
whole  of  North  America,  hence,  as  with  Archean,  it  is  unavoidable 
that  a  single  system  term  shall  be  used  for  the  Proterozoic  group,  and 
as  already  explained,  Algonkian  is  given  this  place.  However,  the 
major  subdivisions  of  this  Algonkian  system,  in  volume  of  rocks  and 
time  duration,  are  equivalent  to  the  systems  of  the  Paleozoic.  For  in- 
stance, the  Keweenawan,  Upper  Huronian,  and  Lower  Huronian  series 
of  lake  Superior  are  each  of  them  parallel  in  volume  to  the  Carbonifer- 
ous, Devonian,  Silurian,  or  Cambrian.  The  same  may  be  said  of  the 
Grand  Canyon  and  Chuar  series.  If  in  the  future  it  shall  be  possible  to 
subdivide  the  Agnotozoic  or  Proterozoic  group  on  a  systematic  univer- 
sal basis,  as  the  Paleozoic  is  subdivided,  the  term  Algonkian  must  be 
replaced  by  Wasatchian,  Keweenawan,  Upper  Huronian,  Lower  Hu- 
ronian, etc. 
COMPARISON  WITH   OTHER   CLASSIFICATIONS. 
The  major  classification  proposed  in  this  paper  differs  in  some 
respects  from  any  previously  given,  although  it  accords  closely  with 
that  advocated  by  Irving,  and  does  not  differ  radically  from  that 
proposed  by  Selwyn  in  1879,  but  afterwards  abandoned.  Irving  did 
not  recognize  that  within  the  formations  called  Huronian  there  is  a 
structural  break,  which  properly  divides  them  into  two  series,  Upper 
and  Lower  Huronian,  although  he  realized  that  unconformably  below 
rocks  which  he  denominated  Huronian  are  elastics,  which  were  sup- 
posed to  be  inseparable  from  the  Laurentian.  As  a  consequence  of 
this  and  of  the  failure  to  appreciate  that  in  this  lower  series,  as  well  as 
in  the  Upper  Huronian,  there  are  abundant  evidences  of  life,  he  ex- 
cluded from  the  Agnotozoic  a  part  of  this  Lower  Huronian,  placing 
it  with  the  elastics  of  the  original  Laurentian.  In  the  lake  Superior 
Lower  Huronian  there  are  carbonaceous  and  graphitic  schists  and 
beds  of  iron  carbonate.  In  the  original  (Middle)  Laurentian  of  the 
East  there  are  great  beds  of  limestone,  regularly  bedded  gneisses, 
quartzites,  quartz-conglomerates,  graphitic  schists,  and  also  very 
graphitic  limestones.  While  the  evidence  of  life  is  not  quite  so  con- 
clusive as  with  the  Upper  Huronian,  it  is  so  strong  that  one  who 
believes  in  its  existence  in  the  latter  series  can  hardly  doubt  its  exist- 
ence in  the  Lower  Huronian  of  lake  Superior  and  the  Laurentian  of 
the  East,  although  no  fossils  universally  recognized  as  such,  nor  any 
hydrocarbons  have  been  discovered.     The  reasons  for  the  introduction 
