388 MORLEY E. WILSON 
trary to the facts, for, while the presence of a heterogeneous assort- 
ment of pebbles in the conglomerate indicates that a great erosion 
interval is probably represented, there is evidence, in some locali- 
ties, that the sediments and volcanic flows are interbedded and 
consequently, if two series are present, it is evident that volcanic 
flows occur in both. In many localities either because of the highly 
deformed condition of the rocks, or because of the paucity of 
exposures, or because of the lithological similarity of the volcanic 
flows, it is not possible to separate these various rocks into strati- 
graphical divisions. For these reasons it seems necessary at present 
to class them together into one group regardless of possible dif- 
ferences in age, making merely such subdivisions as are convenient 
for the purpose of lithological description. In accordance with 
the foregoing conclusion the writer has adopted the term Abitibi 
group to include all the surface rocks, 1.e., the sediments and vol- 
canic flows, of the older complex occurring in the Timiskaming 
region. Since the surface rocks are placed in the Abitibi group, 
the plutonic granite and gneiss must naturally be referred to the 
Laurentian. But it is important to note that the Laurentian 
according to this definition, most probably includes granitic rocks 
of at least two periods of intrusion, as shown by the presence of 
granite pebbles in conglomerate which is itself intruded by granite. 
The flat-lying sediments which rest on the base-leveled surface 
of the basement complex in the Timiskaming region, when first 
recognized as distinct from the underlying volcanics, were called 
Lower and Middle Huronian,' but as there was some doubt as to 
which particular division of the Huronian they should really be 
referred, they are now generally known as the Cobalt series.* 
They outcrop throughout a region extending from the Abitibi 
district in Quebec to the Sudbury district in Ontario, and occupy 
an area of not less than twenty thousand square miles. Throughout 
all this area they rest on a remarkably uniform erosion surface, 
which might be described as a fossil peneplain. 
In the Chibougamau district near Lake Mistassini, 200 miles 
to the northeast of the Timiskaming region, there is a series of 
slightly disturbed sediments which resembles the Cobalt series 
t Ann. Rep., Ont. Bur. of Mines, Pt. II, 1905. 
2W.G. Miller, Eng. and Min. Jour., XCIII, 643, to1t. 
