HURONIAN FORMATIONS, TIMISEAMING REGION. 
3 
for formations and series of formations and it was suggested 
that grouping of these units into larger divisions should proceed 
as a conservative expression of the broader historical facts that 
would emerge from the accumulating data. A classification 
of the rocks of Timiskaming region embodying what was then 
known was presented, and the hope entertained that, while 
this classification would no doubt be expanded from time to time 
as new facts were obtained, such additions might be made with 
a minimum amount of alteration in the existing part of it. 
The substance of that paper is repeated at some length 
because the present one deals with the same subject. It is, in 
fact, one of those anticipated supplementary contributions to the 
classification of the Pre-Cambrian rocks in Timiskaming region. 
Thorough geological field work in Timiskaming region has 
been done, to a large extent, wherever economic developments 
have made such work necessary, and as these localities were 
commonly far apart special nomenclatures were adopted, in 
consequence of which the nomenclature for the whole region has 
become rather complicated. Fortunately most of the formation 
names now in use were first employed in only three localities, 
the Original Huronian, Sudbury and Cobalt districts, shown in 
Figures 1 and 2. Logan and Murray examined the Original 
Huronian area near Sault Ste. Marie between 1847 and 1858 
and gave the names Laurentian and Huronian to the rocks 
found ^ere. Later, the Huronian was subdivided into Lower 
Huronian and Upper Huronian. Coleman has studied Sudbury 
district since 1902, and, as that district is over 100 miles east of 
the ^Original Huronian and contains a considerably different 
assemblage of rocks, he found it expedient to use many new 
names, such as Sudbury series, Ramsay Lake conglomerate, etc., 
instead of, or in addition to, those used by Logan. Miller, 
likewise, has studied Cobalt district since 1903 and for similar 
reasons adppted a third group of names, including Cobalt series, 
Timiskaming series, etc. These different terminologies, created 
to meet the exigencies of geological exploration, have been used 
in neighbouring districts and given more or less widespread and 
confusing currency. One of the first steps, therefore, to be 
taken in composing a general classification of the Pre-Cambrian 
