DEVELOPMENTS IN PRE-CAMBRIAN STRATIGRAPHY 393 
Timiskaming region was originally continuous with the pre-Animikie 
or Eparchaean erosion plane. It also follows from this conclusion 
that the name Lower or Lower-Middle Huronian for any series of 
rocks in the basement complex occurring to the north and west 
of Lake Superior is inapplicable; nor does the limitation of the 
name Laurentian to the older granite in the Vermilion region seem 
advisable, for this usage is not only contrary to the original defi- 
nition of the term, but also contrary to the requirements of our 
nomenclature, since in many localities it is impossible to state 
whether a particular granite or gneiss belongs to the younger 
or older of the granitic rocks recognized to be present in the 
pre-Cambrian basal complex. 
The conclusion that the rocks classed as Lower or Lower- 
Middle Huronian in the region north of Lake Superior are probably 
pre-Huronian in age was reached from two premises: (1) that the 
same series of rocks 1s present in the complex which underlies the 
Cobalt series, and (2) that the pre-Cobalt series complex also under- 
lies the original Huronian rocks on the north shore of Lake Huron. 
By making a direct comparison of the Lower-Middle Huronian 
rocks occurring to the north of Lake Superior with those occurring 
to the south of the lake, this correlation may be tested in another 
way. In the region south of Lake Superior, as in the other pre- 
Cambrian areas, there is a basement complex composed of green- 
stone and green schist intruded by batholiths of granite and gneiss, 
but in that locality the complex is overlain by a succession of four 
rock series. These, named in ascending order, are known as Lower 
Huronian, Middle Huronian, Upper Huronian, and Keweenawan 
respectively. The Lower and Middle Huronian are believed to 
be the equivalent of the original Huronian on the north shore of 
Lake Huron, while the Upper Huronian is correlated with the 
Animikie series of the north shore of Lake Superior. The Keweena- 
wan series, as the name implies, is also believed to correspond to 
the series of the same name on the north shore of Lake Superior. 
These correlations have been generally accepted’ and are almost 
wholly in accord with the criteria of pre-Cambrian correlation, so 
that for the purpose of this discussion they may be taken as repre- 
tR. D. Irving, Am. Jour. Sci., XXXIV, 204, 1887. 
