van  HisB.i  DISCUSSIONS   OF   PRINCIPLES.  493 
below  the  Olenellus  fauna  are  so  enormous  that  the  proposal  to  intro- 
duce a  genera]  term  like  Agnotozoic  as  the  equivalent  of  Paleozoic, 
Mesozoic,  Cenozoic,  to  cover  this  great  groiq)  is  a  conservative  one. 
Irving  foresaw  that  the  term  would  be  objected  to  because  sooner  or 
later  the  life  will  become  to  a  greater  or  less  degree  known,  and  he  sug- 
gested as  an  alternative  for  Agnotozoic,  Eparehean  in  contradistinc- 
tion to  Archean,  which  was  reserved  by  him  to  cover  the  fundamental 
complex.  As  the  character  of  the  life  of  this  group  is  already  be- 
ginning to  be  known,  it  seems  to  me  that  the  term  Proterozoic,  con- 
sidered for  the  i>laee  by  Irving,  but  rejected,  is  preferable  to  either 
Agnotozoic  or  Eparehean. 
In  a  conference  of  the  members  of  theU.  S.  Geological  Survey,  called 
by  the  Director  at  Washington,  these  terms  were  discussed  with  refer- 
ence to  atlas-sheet-mapping,  although  there  was  no  question  on  the 
part  of  any  one  as  to  the  necessity  for  some  such  term.  Recognizing 
the  impracticability  of  the  certain  correlation  with  one  another  of  the 
one  or  more  pre  Cambrian  clastic  series  which  occur  in  the  various 
regions,  and  recognizing  the  fact  that  for  use  in  mapping  a  uniform 
plan  must  be  adopted,  it  was  suggested  that  a  term  of  the  same  class 
as  Cambrian,  Silurian,  and  Devonian  should  be  selected  for  rocks 
here  included,  and  to  occupy  this  place  the  term  Algonkian  was 
proposed  and  accepted.  The  proposed  general  scheme  of  classification 
for  the  lower  part  of  the  geological  column  is  then  as  follows: 
(  Carboniferous. 
t,  ,  I  Devonian. 
Paleozolc j  Silurian. 
[  Cambrian. 
Agnotozoic,  or  Proterozoic Algonkian. 
Arcbean Arc-bean. 
The  introduction  of  the  term  Algonkian  has  been  objected  to  on  the 
ground  that  it  will  supersede  the  older  term  Huronian.  In  answer  to 
this  it  may  be  said  that  Huronian  has  not  been  generally  used  as 
Algonkian  is  defined,  and  it  therefore  does  not  supersede  this  term. 
Huronian  will  be  retained  for  certain  of  the  clastic  series  of  Lake  Supe- 
rior and  Canada,  as  well  as  for  rocks  in  an  equivalent  x>osition  in  other 
parts  of  North  America  and  Europe,  if  such  equivalence  can  be  deter- 
mined, just  as  before  Algonkian  was  introduced.  The  Huronian  will 
stand  as  oue  of  the  great  series  of  rocks  which  together  make  up  the 
Algonkian. 
DELIMITATIONS   OF   THE   ALGONKIAN. 
The  further  back  we  go  in  the  history  of  the  world  for  any  given 
region  the  more  frequent  have  been  the  changes  through  which  a  rock 
stratum  has  passed,  and  therefore  there  is  increasing  difficulty  in  deter- 
mining bounding  planes  with  sharpness,  although  in  different  regions 
rocks  of  the  same  degree  of  metamorphism  may  differ  vastly  in  age. 
