148 ROYAL SOCIETY OF CANADA 
of the extensive unconformity between them; there is a practical 
reason in favour of retaining the old terms of upper and lower Huron- 
ian. In many cases it is difficult or impossible to determine in the 
field which group is actually present, and a general term including 
both will long be necessary in reconnaissance work. ‘This will apply 
also to the Hastings and Grenville series, formerly considered as 
Laurentian, but now properly to be classed as older than the Lau- 
rentian and equivalent to the upper or lower Huronian. Which of 
the two formations they should be placed with is at present uncertain, 
so that here also a general term like Huronian, including both divi- 
sions is desirable. 
Though the difficulties are not all removed we are now closer 
to unanimity than ever before, and possibly a compromise classification 
like the following may be found to serve the present needs: 
MIDDLE AND Jp 
LOWER CAMBRIAN ? (Unconformity). 
OR ALGONKIAN ? Nigeria. 
EPARCHÆAN INTERVAL. 
Laurentian = Fundamental Gneiss, etc. 
(Eruptive unconformity). 
{ Upper Huronian 
or Huronian proper, 
ARCHÆAN (Unconformity). Grenville 
Hurontan- Lower Huronian oe and 
Schistose pyroclastics Hastings 
or , { and eruptives series. 
\ Keewatin Coutchiching. 
