DEVELOPMENTS IN PRE-CAMBRIAN STRATIGRAPHY 397 
time, the Animikie series might be laid down on the same erosion 
surface on the north shore of Lake Superior, as the Huronian on 
the south. If the Lower and Middle Huronian series are not 
present in the region north of Lake Superior, it must simply 
be inferred that they were never deposited in that region, or, if 
deposited, they were eroded away before the Animikie sediments 
were laid down, and that the geological time represented by the 
Eparchaean interval in the region north of Lake Superior is repre- 
sented in the region south of the lake, by three erosion intervals and 
two series of sediments. 
The rocks comprising the basement complex which everywhere 
underlies the younger pre-Cambrian series, have suffered so many 
vicissitudes that although there is evidence, in many localities, 
that two series of surface rocks and granitic batholiths of two periods 
of intrusion are present, yet it is not possible in many places to 
separate the rocks stratigraphically from one another. For this 
reason the only regional classification practicable at present, is to 
divide the complex into two divisions according as to whether they 
belong to the plutonic or surface types. For the plutonic rocks 
the name Laurentian has been generally used, and while this name, 
according to the original conception of Logan, might be more 
properly referred to the whole basement complex, it has since 
been referred to the plutonic types so constantly, both by Logan 
and by his successors, that it seems best to use it with that signifi- 
cance. For the surface rocks of the complex, the writer has used 
the name Abitibi group in the Timiskaming region, but this proba- 
bly corresponds to the Ontario system into which Lawson grouped 
the Keewatin and Coutchiching series occurring in the Lake of the 
Woods and Rainy Lake regions. The subdivisions of the base- 
ment complex (Archaean) according to this classification would 
thus be as follows: 
HURONIAN 
PRE-HURONIAN PALEOPLAIN 
( Younger Laurentian granite and gneiss. 
Laurentian 
Basement | Older Laurentian granite and gneiss. 
Complex ; 
Ontarian or ( Composed of at Jeast two series, to be given local 
Abitibi group { names where subdivision is possible. 
